This is what I'm currently doing for my Vintage Newcrest Save, so you can maybe get some ideas from this. You can just do certain sections of this, depending on whatever sounds fun to you.
Start with 2 premades.Take 2 premades (or maxis-made sims from the galleries), age them up or down to young adult, and get them engaged. Create immediate families for them with their DNA, 2 parents and 1 sibling. Delete all other premades in the game. As your family progresses, pick one child to be the "heir" and marry that sim off to a premade; everyone else in the game is an NPC (but you can make the NPCs over, of course).
Give the 2 main sims 2 to 3 friends of their own. Pick NPCs (single or with a family) and make them over to be the friends. Have them go to the wedding and do activities with your main sims, like friends would.
You can make more minor characters from the NPCs as needed (such as someone to be a front desk clerk, or someone to be a rude guy in a club).
Develop the background of your characters. What type do they embody? (manly man, rebel, socially awkward, etc.)
What is their main function in your story? Everyone that isn't the 2 main sims should have a function that affects the main sims. For example, the rebel sim in my save has the function of pushing my more conservative main sim to do things he normally wouldn't. The socially awkward sim has the function of adding interest and conflict to the storyline by blurting things out that other people won't say.
What are some key childhood and teenage experiences?
What is their woohoo history? Likes and preferences?
What are their hobbies (may or may not be something they can actually do in the game).
Pick a timespan.My save takes place in the timespan of 1930s-1960s. It is forever and always those 4 decades all mixed together. The buildings, clothing, and social mores all reflect this. (It's pretty easy to do furniture and buildings from the 1900s without having to go and get a lot of cc).
Have them all live in the same town.I have mine live in Newcrest. One section is residential, one is commercial, and the other mixed. Because of the lack of space in the neighborhoods, I try to give most of my commercial lots at least 2 functions, even if one of them is just for screenshots. For example, your library can also have a plaza in front of it where people can sit and relax.
Not everyone has to have a house. I just stick some of the friends in a random house in another neighborhood to have access to them but never show them in their home. Other characters are homeless.
Give them jobs you can follow them to.Almost all of my sims are unemployed, but they all have jobs in the neighborhood. I sometimes use clubs to get them to hang out where their job is, or I take them to work at an office I've made, or I have them technically own a retail store but in the story just be the manager there.
Move supporting characters in and out of your sim's main house to complete tasks with them and control them. For example, when my receptionist goes to work, I move some of her coworkers in so I can control them when they're at the office, then I move them out when the work day is done.
Make a list of things you want them to do each season.Now decide what you want them to do each season, make screenshots, and let their actions and the backstory you did for them guide you in what they would do next.
For example, during winter, I wanted my sims to experience the first snow, go ice skating, exchange gifts on Winterfest morning, and do something with the family on Winterfest.
For each of my seasons, I want to make sure I include something romantic, something with friends, something with family, and something with conflict.
An example of letting the sims' backstory and actions guide you is my character Gavin Todd. I made him as a very minor character to show sexism in the office by being one of my main sim's boss. But then that led to me making a scene with her telling her husband about it when they sat down to dinner, which led to a scene of the husband having a confrontation with the boss in a dark alley, which will lead to more future confrontations. I didn't plan all this, but I let the characters and story dictate the next thing to happen by asking what they'd do in that situation.
It helps to have some basic mods.MCCC will let you change the weather, season, sim's mood, and all sorts of things, and is super helpful when doing this kind of gameplay. I also like mods that add personality, such as slice of life.
EA didn't make the sims to be "real" enough, which is why I think people get bored with it, so you have to make them real through imagination and storylines in whatever way you want to do that.
You can see my save in action if you search for "Vintage Newcrest" in the
Stories and Legacies forum on this board. Start with page 2 (that's when I clued in to using dialogue.) (I can't link directly because I change the title when I update, so the url changes.) Or you can just
view it on Tumblr.