For the base game, try filling out household collections (Fish, Space Rocks, Metals, etc.), making money with stay-at-home jobs like writing and programming to make more time for exploration and social activities, making a sim who's a troublemaker who goes around causing chaos around the town, or any of the various challenges that people have created (or, make up your own unique one).
For "Get to Work", try playing an alien, get a sim pregnant by aliens multiple times and have a bunch of alien offspring to raise, open a store, or play one of the active careers in an evil or incompetent manner (scraping by just enough not to be fired).
"Vampires" adds a lot of options too. If you make a vampire with the "Chief of Mischief" aspiration, then give them the vampire ability that lets them just break into people's houses, you can have him/her go around town in the dark of night, breaking into people's homes and clogging their drains. Add the "Kleptomaniac" trait, and you have yourself the perfect criminal! *insert evil laughter here*
Also, just diddling around in build mode and trying out new housing designs is fun too. If you're stumped for ideas, you can find, like, billions of building tutorials on YouTube.
For an extra boost, install MC Command Center and tweak a few settings to get your in-game environment and population just right...
The real key with making and keeping this game fun is to examine the tools at your disposal and find new ways to use and combine them to your liking. Don't be afraid to use cheats and mods either, since they can come in handy for setting up certain scenarios. For instance, everyone knows about the "Motherlode" cheat that you can spam to make your sims filthy rich, but there's also a cheat for taking money from your sims so you can start them out dirt poor! Look deeper than the everyday grind of work, school, and family to find the hidden nuances and tricks in the game.
