Many times when I get a new pack, I will make a sim or household that fits the pack. For strangerville I made a military sim with military hair cut and clothes, gave him traits and aspirations to fit him. For realm of magic I made to 2 twin spell caster sister, but one with white hair the other with black, one with a dog, one with a cat, one spell caster,one a potion maker, gave them a special house.
Make a back story for you sims. Are they rich or poor, smart or goofy? What town are you going to put them in, has their family been there for 200 years or are they brand new to the town? Are they going to be a famous musician, or a Doctor, or own a special business? Decide before playing what kind of skills they are going to build. If all your sims cook, make one that goes to the grocery store and buys ready made food, orders pizza, or eats cereal, or better yet goes to all these ready made food places and takes out orders. Are they going to be an extrovert going to all the festivals, or a loner who prefers to stay home? Rotational play is fun for me.
Or take a look at the sims you have, and then choose a different facial and body features than the ones you currently have. Give them traits you wouldn’t normally give them.
Make a different household type than you have... a 3 -4 generation family, a single parent, a grandparent with grandchild, (make the parents then, delete them or put them in s separate household as townies, put them in a house if you don’t want to lose them). Think of a different cultural type than you have, make them according to that.
Watch youtube videos of people making sims or households. I learned features that were in cas I either didn’t know were there or had forgotten existed.
Use the randomizer till you find a sim you want to tweak, one that looks different from your other sims.
Sometimes I even find a townie I want to be mine, give them a make over ( look at their traits and make my own back story for them ).