You have to be careful with the term 'Nice guy'. People who are new to this whole thing, the world of self improvement, meeting women, etc etc - are easily fooled into PUA material and all kinds of 'anti nice guy' stuff - some of which they are misinterpreting.
Nice guys get laid. You don't have to be a prick to get laid. The problem is, guys change their personas when they meet women to meet their needs - sucking up to them, feeding their egos and becoming lost little school children - this is what is commonly referred to as being a 'nice guy' - when you're that guy who meets a girl and then very quickly tries to close some kind of deal by being very lovely and sweet and offering to do every little thing for her - and then this same guy gets rejected after basically being like a sexually turned off child friend to this girl - and THEN has the nerve to complain that it is because he is too 'nice'.
And that's where the problem comes from. 'AFC' behaviour is as mentioned above. It's when you turn from being the interesting, fun guy that you are, and then when you suddenly meet a woman you can't talk properly, suddenly your hobbies are exactly the same as hers, suddenly you're paying for everything, suddenly you're moving around your schedule to fit hers.
This is what guys have to get into their heads: You are in YOUR world. She is in HERS. You two are not exclusive yet - so be YOU. Be that guy. Be the guy that is interesting, busy, spending time with friends, and of course meet women but don't change your entire being when you talk to these women. Don't become somebody you're not, don't dumb yourself down. Tell things how they are. Don't be a puss.
You don't have to be a jerk. You can still be charming and funny and interesting, but you have to be honest. If you're NOT a charming and funny guy - you can work at it, but you're not that guy, and if you try and pretend to be, you will look like most wannabe PUA's out there, out of control, out of your depth.
The real answer is in working on yourself and this stuff takes a long time. But here's the thing, each of these tiny adjustments you make to yourself and your social setting and your health etc make a huge difference in how you are percieved socially.
It is unbelievable how drastic the changes can be once you finally start to put the pieces together. All that time spent reading, learning, thinking, hitting the gym, getting good clothing, getting friends that are actually interesting, becoming well read, learning to speak properly, blah blah blah - you combine these things over time and suddenly you're a real catch - or at the very least somebody that's going to get some female attention.
The nice guy moves too fast and too slow at the same time. He's quick to try and close a connection, in the sense that he'll do a lot of texting that isn't flirty or sexual or anything, he'll be around all the time no matter what, he will hide his true identity, if he's busy he'll say he's free so she thinks he's just always free and ready for her every need - he won't make any clear sexual advances early on, so by the time he makes a bad 'move' (usually in the form of 'I really like you, blah blah blah', it's way, way too late).
There are obviously more subtle versions of this that I don't have time to talk about - but you get the idea. You're a man. Love yourself. Change the parts you don't like. Invest the time. And it takes time.
Look when I first read all that PUA stuff back a few years ago, you'd read something like 'fix your wardrobe' - and that's cool - and in that state of mind I thought I'd fixed it. Now I look back and I realize how stupid I was. But that's because it took more than just me being like 'ok' and trying what I thought was the fix - you have to work at it. You have to look around and see what people are wearing and really work and try it out for a while before you find the right things for you. And the same thing is true for everything - personal development, meeting people, the gym, whatever.
So I guess after all this blabbering what I'm saying is - don't worry too much about what a 'nice guy' is or a bad guy is - you worry about improving yourself and taking notes. Okay, so on one level - if I had to put it this way - back in High School I would NEVER have made a joke or said an 'out of line' comment or spoken my mind to a girl I was into - because I was an insecure little baby who put women on giant towers and didn't know how to climb up there.
But now? Now I'm me. I've always had a bit of attitude and said things that most people consider to be risque (but funny) - and I managed to be very popular among guys - then one day I realized when I was meeting women I was becoming this boring guy who didn't talk the same way when I was with them. This was me being an "AFC". Nowdays I pretty much treat women I'm into the same way I'd chat to a guy - I joke, I tease, I make fun - but here's the kicker - NOT for game. This is the point you need to understand. It's NOT game. It's just me being my natural self and not being afraid or embarrased of who I am. And it works...more than you could ever realize.
The most recent example I have is the other night in a club a very attractive girl asked me if I'd buy her a drink. I said No. But you can buy me one! She had never done this before, but she ended up doing it anyway and I closed the deal. In the back of my mind I remember this kind of thing in PUA material - and it is. But here's the difference: when you read it like that in a book and try it out because it says to try it out, you're going to look weird and not confident and just out of place saying stuff like that. But when you actually get to that point when you're responding to girls like annoying little sisters or your friends - then you will realize this stuff just comes naturally. Because it really does eventually.
I guess it's the 'un-natural natural method'. Who knows.