When I'm not making a completely original Sim, I take inspiration from characters I see in television or other media, though I never have my Sim share the character's/actor's name as I still want them to be their own characters. And depending on whether I get extra ideas or not, I'll either stick to the theme that character has or mix it with something else. For example, I just recently made a Sim based on the appearance of Ariel Winter, who played Alex from Modern Family. I have another Sim whose appearance is inspired by Ymir from Attack on Titan, but I also made her a Werewolf and I made her while asking myself the question of what I think would be the kinds of outfits Ymir would wear if she lived in our modern society, but as a Werewolf.
However, my main Sim and the Sim that's the protagonist of my story is completely original in appearance. I also have a personal rule to avoid downloading other people's Sims, even if I like their design, and instead I try to replicate them with my own spin.