I make a lot of occult or fantasy sims, or really ridiculous looking ones. I'm not very good at making real people, so I just have fun with it. Sometimes I do stick with a theme/make a sim based on the title or lyrics of a song.
I am terrible at making male sims, I can never get chins and jaws right so I mostly stick with that I know. The males might look *right* to me in CAS but when they start having kids I'm like "Oh my, where's that kid's chin?? Why does that child's face look like melting marshmallows?"
Any time I've tried to create, I guess, what might be considered, an attractive sim they come out looking so wrong I end up creating something purposely silly instead to help with my frustration of not getting the look I want.
I made a spellcaster inspired by one of my cats a couple of days ago. She's sick and on that particular day, her test results came back better than I expected and I was over the moon. Because the sim is based on my cat's features I gave her some exaggerated looks. I think she still resembles a person, but she has big pointy ears, cat shaped eyes, those kinds of things. That's why I'm better at occult and fantasy sims, because they can be as realistic or unrealistic looking as I want.
As far as what to wear, I think of who it is I'm creating. I once made a sim based on a song and I based her color scheme and outfits off the album artwork the song came from. I do put little details and touches like that in.
Fantasy sims usually get put in medievally stuff, but not all my occults do. I tend to dress spellcasters like every day people. One of them dresses like your everyday soccer mom. Vampires, I normally go for a mix of modern and classic styles.
If they're merfolk, I usually go for island attire because I wouldn't play them outside of Sulani as it's easier for them to go swimming there.
Regular sims, it depends on their personalities. I make a lot of hippies or rock n' rollers, sometimes I make preppy sims or ones who like designer clothes. It depends on who they are.
I love making sims, but I have to be in the mood/inspired to. I'm terrible at building, but I do enjoy making new sims when the mood strikes.