I don't take requests, I barely have enough time to draw my own art!
However when I did do drawings for people I avoided anything obviously against my own moral code or horrible.
I draw violence and gore to a point, but I stop when I think it's becoming exploitative or needlessly horrible (for example, while I appreciate his talent, Jacen Burrows type stuff is WAY over the line for me. Do not Google him if you have low tolerance for explicit gore).I like stuff that's kinda macabre though, a good example is the old horror comics and the excellent (peerless some would say), work of Bernie Wrightson.
I also don't like drawing too much anime inspired stuff unless it's got some streak of creativity to it. I got one or two "Draw my 4000 year old demon OC who's actually an angel but was kidnapped at an early age and sent to a Japanese High School" requests which I turned down.
I'm thinking of starting up again though. I've been practising on some fan art of well known characters to get back into the swing of things.