I focus a lot on the community aspect. I fill my game with locations and events that might require some imagination, but that helps me form the community. It's like a huge everlasting puzzle. I switch active households often, and with the community background it's not very important who I play. This way I get variety, too.
I run a Council House, every 5th year there is an election, and the 5 Councilors are given either Department Law & Justice, Trades & Taxes, Culture & Entertainment, Health & Welfare or Science & Education. One of them (most often the one at Law & Justice) will be the Mayor.
I don't necessarily play out the Council in detail, but I found this routine to work well when I want to add something, or to make sure existing routines are kept active. Say, when I want to build and equip a Retirement Home, the Health&Welfare Councilor will take the job of organizing it.
I also have photographers specializing on family portraits, celebrity promo portraits, or even pet photos. Any sim who has a job will specialize according to the community. Say, a sim will not just be in the Business career, but will also have defined goals and tasks - like working with timber import, happy to reach level 5.
I have a social status system too, making it a bit harder to find spouses. Most high status families will want to secure their status through the main heir's marriage, and those on lower levels might dream of climbing a bit.
I have a very old tradition when naming a baby, a system I used ever since TS1. In short, the baby gets first and last letter from grandparents, but whatever in between is open. There is also a system to pick traits, securing that most kids will get one trait from each parent - but not always.
All in all, giving my sims (families) a community function, some history and some hopes for the future, makes the game feel more established. Even if I take a few weeks break, I know most of the residents pretty well, and can quickly look them up in
my residents registry, too.
PS: There are several videos with more detail from how I play on
my Youtube channel. The "As Sims Go By" series is based on my Council.