Guys.. chicks be crazy. That is the lesson to learn. One thing my old friends mum used to say was "when someone shows you how ugly they are inside, believe them". Do that with everyone. If someone is a bitch around you about someone else, what is to say they won't be a bitch about you to someone else. Do not stick your dick in crazy. Do not sympathy fuck a girl who just got dumped, no matter how hot she is. Do not help someone cheat. Do not be nice to a girl and expect anything from her. Do not assume she's a slut if she dresses slutty (though if she's showing cheek and it's 11am on a weekday.. well).
Just use your common sense. Always have the headspace to be able to take a step back and assess the situation. At the same time though, don't overthink every single situation.
Also, this is just anecdotal evidence from a guy who has been in a relationship for nearly 6 years. This is anecdotal evidence of anecdotal evidence, so take of it what you will. Also my advice has nothing to do with being a player.
edit: reading back on everything i wrote, its all a mess of shit. its not advice in general, just don't scare her off by being overeager or being too aloof. if you want to hang out with her, do it. plus guys, if he really likes her he won't listen to a fucking word any of us are saying to him