I'm a massive storyteller in real life so the sims is yet another platform for me to express my imagination! :)
Whens starting a game I love to create couples based off movie characters. They never turn out to be anything like their movie prototypes but that's not the point, the point is to get yourself some good-looking sims without breaking too much sweat! :D Then I give them an interesting (though mostly basic and cliche) plot and see where it goes from there. Sometimes I have a huge story arc completely thought through, I know exactly where my sims will end up in two weeks and what are their plans for next year. But mostly all of the main twists come to my mind during gameplay or taking screenshots.
I'm a realistic player, which means that my sims have to brush their teeth, pay insurance, get haircuts and do a lot of other unnecessary things. I don't even allow them to travel to different worlds without using the plane or the train! And tickets cost a fortune. Also, before starting a game I think about how much money, what skills and what jobs will my sims start off with and cheat all of that in to make them more real and lively from the start. I find it very unrealistic that all sims start off with only 20 000 simoleons and no skills whatsoever.
My sims have a custom lifespan of 840 days. One year equals 84 sim days (I play with 21 day seasons) and equals 7 years of growth (basically if a sim is born in spring he'll be 7 years old next spring, and 14 the spring after that), so in total they live 70 sim years. That's pretty long, but I never get bored with my sims. I sign them up for classes, send off on a cruise to Disneyland, add more drama to their lives or simply switch to another family. And there's nothing wrong with having boring routined days once in a while.
Overall the plot, the story, and character growth are the main things I'm invested in when playing the sims. I play stories, not challenges. And it's fun. :)