I don't give out a lot of compliments in general. But when I do, I've had better luck complimenting people on appearance when it's stuff they obviously chose and put effort into: a haircut; tattoos; choice in clothing. Few people like to be complimented on stuff they didn't do anything for; many people like to be complimented on stuff they did.

(If you try clothing, though, be aware that "nice top" is likely to be read as "nice breasts".)