My best advise to men is to know your size! I used to work in men's fashion and it would kill me that most men have no clue what size they really are. If you wear clothes that fit they lay better on your body and actually will literally last longer.
I don't know why some guys think showing off their underwear is cool. What makes them think that a protruding boxer short or CK brief is anywhere near sexy? It looks tacky to me. Justin Bieber and his sidekick Lil Za used to look like complete idiots sporting this "trend." Anyway, it's more sophisticated to keep your underwear under wraps.
I have been wanting to say this for a while now, because it is something my boyfriend does and drives me CRAZY! I hate it when grown men put on shorts and then tennis shoes with high socks on. I think it looks really bad, not age appropriate and just weird. I wanted to tell my boyfriend I hate it when he does it but could never actually mention it to him!
Hygiene and neatness would definitely be on top of my list. I don't really care if a guy is wearing something branded or high end, as long as he is neat and clean all the time, I think that's what matters the most. I really hate it when guys look like they haven't showered for days and they have the audacity to actually go out like that and even try to get a woman's attention. It only goes to show how irresponsible that guy is, because even himself, he couldn't take care of.