If you are used to playing normal or "nice" sims, change it up:
Make an evil family or club and just go all out with being evil!
Honestly I hardly ever play truely evil sims but when I do, it's so much fun, tormenting the worlds.
For example my evil doers had high aspirations becoming a crime boss, becoming mayor etc. basically everyone had to become somebody with power/influence.
Vampires come in handy for that but they're not needed.
Build venues with the mean vibe and grody traits, restaurants with the grody trait are especially wonderfull >:)
Make a family/ household with only bad mannered sims, lazy, mean, evil, erratic and so forth.
The goal won't be to turn children into wonderful adults but the opposite, they should get all the negative traits from parenthood when they turn into young adults.
Build themed venues where you have to use sims (their skills) to fill them up, for example, I am currently building a museum for the abstract art so I have my painter sims paint abstract paintings like crazy till I got ALL of them plus the quality has to be at least excellent (gonna do this for other painting styles as well).
For me it's the mix of building and playing that really does the trick to keep me interested and always finding new things to do, or old things to do differently.
Sometimes I have a specific idea for a venue but no played sims that would fit as visitors, so I create new sims that would go there and the other way arround.
I have sims collecting only what fits them, for example "spooky" sims only want the spooky fish in their fishtanks and for some of them you'd need quite a high fishing skill (anglerfish), my "nature"witch really needed the treefish, same thing.
But I never do everything with the same sim, hmmm...maybe if I ever want a "Supersim" so to speak, but it would bore me cuz there is no point for me, my sims all have their own characters by which I decide what they do, it's more diverse and more fun for me.
And I also have all my households know each other, for now they are all friendly, since my recent game has no evil sims yet but that will soon change (evil mermaids!).
Anyway, I don't know if this helped, maybe hopefully...just do what you like, it's a sandbox game after all ;)