It is a device I often use when writing a novel set in an alternate history universe - I mentally go for a walk. I take a character on an adventure in my mind around the city he is staying in, away from the plot, away from complications that would derail the plot, and I simply imagine him having a day off, so to speak, a day to himself wandering and experiencing life. It won't necessarily be as something strange to him, though it may be, it may in fact be a perfectly ordinary day wherein he simply conducts leisure, past-time and utilitarian activities, things that would be 'off-screen' if the novel were a film.
Imagine your character's day, perhaps, as if it were to be an analogue of your own day off. The character lives somewhere he knows, he has errands to run, he has fun to seek out, he has a mixture of people he will meet during the course of that day - some strangers, some he knows simply because they are always there, some he knows to nod at or say good morning to, and some he knows well as friends, to stop and spend some time in conversation with.
Such a mental device seems at first to be mundane - of course there will be shops, taverns, newspapers, vehicles, what have you. But look further and this will bring colour and interconnected realism into your novel. That last phrase may be a bit of a mouthful, but it means to step beyond the plot device of describing the villain's alternate history car, but never bothering to fill the reader in on the rest of the road traffic, or to describe in detail the peculiar shop that the character has a vital assignation in, without explaining which seemingly strange details are in fact commonplace, and which are unique to that place.
Give yourself as the author an idea of what is normal and everyday for the world that your character inhabits by taking him for a walk around it.
Let us consider an alternate history novel set in the late 1960s in a Britain that diverged from known history with the death in childhood of Princess Alexandrine Victoria, meaning that in 1837 it was her unloved uncle Ernest Augustus who took the throne as King Ernest I of the United Kingdom of Great Britain and Ireland, and of Hannover. It may seem extreme to give us a hundred and thirty years to play with, but we are not concerned so much with the history of events between these dates, but at how that history manifests itself in the everyday life of our character.
He gets out of bed in the morning, and how is the room? Is there a portrait on the wall - of a monarch, or a president, or a dictator? If there is, does he acknowledge it in anyway, or does he ignore it? He uses things like soap, toothpaste, coffee - what makes are they, what is their packaging? Are they sold in bland containers, or in highly colourful ones replete with advertisments? Are there paintings or artwork on their packaging, pictures that would be an everyday sight to a character in this world, but would jar if one were seeing this on the screen, or were as the author teleported in from your own reality?
What is for breakfast, or does he not make his own but heads out to a cafe, inn or some other place to eat? If it is an inn, there are no early opening laws, are people drinking beer early in the morning, are some drinking, others eating? Whilst you may find this in any city centre Wetherspoons these days, just ten years ago it would have seemed an amazing thing from our OTL perspective. Is it something that is normal and from time immemorial for your character and those he associates with?
What does he pay with? If notes, what quality is the paper, what colours are printed on them, what pictures, symbols and portraits can be seen? Is there a current monarch, or are the notes depicting famous people solely from the past? What is the denomination, and the currency - is it a five pound note, or a hundred crown note, or perhaps a ten thousand dollar note? If it is coinage, again what colour, size and shape are the coins, are any bi-metallic, do any have holes in them or be of a non-round shape? Are the metals shiny or dull, are they true coins or tokens instead? Perhaps the payment is by some other form - on account, or a tab, or maybe by telephone call to a bank where a security code verifies the transfer of money? Is there a credit card of some sort, a system where an imprint of the card is sent to the company who then pay the innkeeper whilst billing the character? Does technology allow anything more complicated than this?
Are people smoking, chewing gum, spitting tobacco out on the floor, taking snuff, lighting a joint, shooting up with heroin in plain sight? Does the bar provide newspapers free to customers, or perhaps sell some to them, and does the character read about the world's news or look instead to celebrity tittle-tattle or the sports news? The latter is often ignored in stories, whilst being very important to many people most of the time. Perhaps he reads of an elite level motorcar race, maybe looks for news on his favourite driver or team, or perhaps there has been a crash and a death, certainly in the past a far more common experience than it is today.
Are sports like football, rugby, tennis and cricket major ones, and if so do the rules resemble those we know today? Perhaps a unified sport somewhere between football and rugby has emerged and he reads of his favourite centre forward lunging over the goal line with the ball in the crook of his arm? Details like this would be easy to miss, but the historical development of sports is never a unified path and can have easily been knocked off course - for example if Ernest Augustus' rule led to a Republican Revolution that overthrew the monarchy in the mid 1840s, that abolished the great public schools and brought about education reform at so early a date, the playing fields of Rugby and Eton would never have led to the development of games we take for granted today. Instead the village tradition of mass-gang football/handball games could have transformed itself into an orderly sport that was now played universally where-ever the phrase "football" raised its head.
If he even glances at the celebrity news in the newspapers who are they? Are they singers and if so what is the prevailing fashion? Has history led to it being some kind of celtic folk dance rather than the rock and pop of OTL, or is it all still big bands and crooners; maybe lively piano playing singers in garish outfits, or something entirely left of centre, all-drum outfits with rhythm and no words? Are they filmstars, and if so where is the centre of world film-making, or is there not one (no equivalent to Hollywood) just a number of primary centres based in the major film-making nations of the world?
Names are always useful handles to drop into a story later, or even into a detailed timeline for colour, so who does he follow in motorsport, what is the name of the driver, the team, even the team owner, what is his football team also? The latter can also be a vehicle for showing different municipal and industrial development during the course of an alternate history - if Aston is the name of the city and Birmingham a suburb of it, rather than the other way round, what stopped the trend away from this being the original state of affairs (as it was) towards the prominence of the name Birmingham? If the main football clubs include places such as Nelson and Southport, were the North-West of England even more important industrially than historically? Perhaps cotton never suffered a crisis and the region continued to grow? Does that in turn mean there was no American Civil War, or perhaps a peaceful secession of the South?
What sort of films are the filmstars he is reading about starring in? Are they dramatising events of the past, and if so this would help add some details to a timeline, or to a popular interpretation of the history of this alternate history - what for instance do people consider to be the major events worth turning into a film, even if they are but parts of a far more complex story? Was there romance there, or the do-or-die exploits so beloved of films, or perhaps there is pathos, or a tragedy that needed telling? Are these films in colour, are they made in Britain, or imported from abroad, are the filmstars British or has this aspect become internationalised?
After finishing his meal and his pint he returns the paper and leaves the inn (to give answers that reflect a narrative in this example, rather than to admit of all the other possibilities for each question); where does he go then? Let us say it is a weekend and he has no work to go to, no major plot element he has to develop, and thus no greater imperatives than what he would do when left to himself. The inn is probably near to his home, and he probably needs to buy some things from a shop - most of us, most of the time, need to do this, even if it is only those few items which we have forgotten. What sort of shop does he go into, what sort indeed does he have the choice of, are they in fact free entry or do some shops charge an entry fee, or others require identification or the handing over of some sort of passbook for entry?
Is it self-service or do you queue to ask someone behind a counter to get what you need? Does he buy candles, and if so does this imply that the electricity supply is prone to fail from time to time, or that he is restocking after a perhaps unusual power cut? Does he buy much food or is the general culture to eat out most of the time? Does he look at things for sale and wish he could afford them, or had a need for them, but dismiss them as luxuries - what are these things? Maybe they are pineapples and we can see them as priced each beyond the total cost of his breakfast and ale? Or perhaps they are toiletries, aftershave perhaps which he would like to be able to buy but does not see how he can justify the expense? How does he pay - the same as in the inn, or is it a different way for a shop, and are there are ration coupons, or membership cards or club points in play?
Let us say he returns to his place to put the shopping away, or leave it untidily on the table whatever fits the character best. Does he go straight out again, does he turn on a radio or a television, or is there neither in his home? Is it colour if there is in fact a television? If he has bought confectionary does he eat any, what of the packaging, branding and advertising? A major difference in society would be marked by chocolate bars that come in plain wrappers with no advertising on them as against those in coloured paper resplendant with script and pictures. Which best suits the world that your character lives in?
He goes out again - is it to an inn, to a library, or to a sporting venue? Maybe he meets some people in the street whom he knows; who are they, what are they like, how friendly is one in the street? If there is a woman do they kiss on the cheek, or perhaps snog full on in front of everyone, with nobody taking any notice? Is there an official, and if so is he armed? Do gendarmes walk the street, or uniformed bobbies, or is it unclear who is the picture of the authority on the streets? Maybe there are cameras, maybe there are a corps of plain clothed watchers mingling with the crowds, maybe there are soldiers at strategic points, watching, able to gun down a suspect from afar or come surging out en masse should the crowd turn into a mob with aims more political than sporting?
What sport does he choose to watch? Is he mixing with friends, or with acquaintances or is this not an altogether usual thing for him to do and he has come on a whim, or perhaps just to see an important match, or a famous player in one of his last games? What is the home team called, what are the visitors called? What colours do their fans sport, what chants rise around the ground, what obscenities are screamed, do they sit down or is it a packed and crowded standing area?
If the home team loses is there a riot, are the police pro-active, or are soldiers on the street in armoured vehicles to deter anyone from protesting too voiciferously? Is the talk on the way out of referees or linesmen, or of bloody vengeance that will be wreaked against the fans of the opposing side if only the soldiers would let them at them?
Does the character go home, or to an inn, or to a brothel or a sex show? Perhaps he goes to a street theatre performance, players and music licensced on the corners or intersections at weekend, but what plays are they performing, what music is being played? Are there large crowds or passing interest, is there a carnival atmosphere or is this every Saturday night, something to stop and watch a while before moving on? Are there soldiers or police around, or is everyone in good humour, despite the earlier sporting defeat?
Does he end the evening in an inn, or at a brothel, or does he go home and watch the television or perhaps listen to a radio drama? Many questions could be asked about each option, not least the brothel, but by this time in the exercise these questions should be springing to the front of the author's mind automatically without the need for further prodding.
This is only one example of "A Day In The Life Of"; other examples perhaps in other settings, other periods, with people of a separate class, could take a drastically different path. But the general effect would be the same, the answers to the questions as to what is normal, what is the usual background, how are frequent events responded to, and so on.
Some of them will soon find their way into your novel or detailed timeline, others will sit in the front of your mind as you add different colour and detail to your scenes, creating this interconnected realism even without referring specifically to details that you have now accepted as canon for your alternate reality.