The Sims that I create are completely different than I am. If I ever played with my simself I'd be bored as plum, lol. I also don't make characters from TV or films or books. I just create random characters.
I create both regular Sims and occults, but more regular ones. I start with randomizing a character and once I see a one that I like I start changing their face and body. I usually know how I like my Sim to look like, sometimes pretty/handsome, sometimes average and sometimes unique. I have a lot of different characters. I like to randomize the traits if I don't have a specific story planned for her/him.
I choose the clothes that I think the Sim would wear. I'm not a fashionista, I don't spend too much time choosing their clothes. It's the easiest part on creating a Sim. Adult males are a bit more difficult to dress, because the choices are so limited (I don't use CC), though.