Have you given him equal amounts of attention back?
Perhaps this is common sense, but if the guy is giving you a lot of attention but you're not giving back to him anything, then eventually he's going to think you're not interested or don't appreciate the things he does, and pull back himself.Before asking yourself what you're doing WRONG, ask yourself what have you done RIGHT? Have you shown him how much you appreciate him, have you clearly expressed your interest towards him and ENCOURAGED him to continue to pursue you?

Pushing the guy into action?
Sometimes us women want to make sure that guys know what we want of them. Sometimes this can be seen as being "pushy". If you've being hinting, nagging or complaining about something they're NOT doing, this is a sure way to make certain they're going to pull away. Guys don't want to be pushed into doing things for someone they'r interested in. They must come to their own conclusions about doing something, and take action because they really want to. If you push, even if he was going to do it anyway, it's going to turn him off taking action. So, if you feel you've been nagging him about something or even "hinting" you wanted more from him, it will have inadvertently made him hesitant to do those things.

Giving him too much attention too fast.
It's common when you first get into a relationship and really like a guy, you just want to be around him all the time, tell him how much you like him and do all sorts of romantic things for him. Although this is how women express their love for someone, guys will feel smothered and wonder if this behaviour will eventually lead to "jealousy issues" or you preventing him from "doing his own thing". If you feel you have been smothering the guy too much.. calling too often or showing more interest than he is, then you need to pull back and "allow" him to chase you. Remember, guys do like the chase, but he can't do that if you're constantly making the move for him.

Giving him too much power.
When you give a guy power, he can then choose to call you or show you interest only when HE feels like it. Men are smart, if he has a good casual thing going with you, but don't want a full on relationship, he'll be hot and cold with you to ensure that you still stick around when you need him. If you always make yourself available to him and give the impression you don't have anything else going on in your life except waiting for him to call or ask you out, this is giving the man all the power to do what he pleases.

He calls when he wants, he ignores you when he wants and he basically has a sweet deal. Do NOT be subjected to this kind of treatment from a guy. If the guy just isn't that into you, then he isn't into you and you should just move on! There's plenty of men out there!