Others may have touched on this already... but seeing the "nice guy" thing in the thread title makes me want to caution others not to misinterpret.
Women love "nice" guys. Being a kind gentleman rules... That's exactly what most of them are looking for (unless they're the kind of trashy mean party girls you only ever see in highschool and cheap clubs, before they've grown up). Women would love a nice, upstanding man, who knows how to take care of them, and do honorable things.
Basically if you still have the juvenile "The Game" fantasy that girls only like asshole gangster boys... think again. That's a fantasy. It may be one tiny part of hook up reality (yeah I know gangster kids always find it easy to pick up dumb sluts), but most people are not hooking up like that.
Being "mean" or "self-centered" or even "cocky" will probably do nothing for your pickup ability. It's an absolute red herring. It won't help you at all.*
*(unless damaged girls who have daddy issues, and love being abused, are your prime target)
But of course, while women love "nice" guys.... they probably won't like "nice guys". ie doormats with no clue what they want, and no personality. The term "nice guy" refers to a kind of stereotype that we can all understand, of a kind of spineless man... but make no mistake: he wasn't actually pathetic because he was nice. There was nothing wrong with him being "nice" when it comes to picking up girls. It's just that, with no strength in his personality and character, being "nice" was the only thing you could say about him...
You should probably be a person of character who goes for what he wants. But being nice/mean? Has nothing to do with it whatsoever.