I recommend a trait randomizer, and possibly a number randomizer to see how many sims in your household and what traits they have. I've found that builds story for me. Try playing things you haven't before: evil genius sims with a serial romantic trait. Getting out of that rut is about starting different.
Also, set some goals or challenges for yourself, or follow a challenge someone else has made. It's a great way to feel like you've accomplished something. Sometimes sandbox games need a bit more structure to feel worth your time, and I 100% get that every now and again.