Smile. Guys desire a girl who is happy. If you are bold with your happiness by smiling and acting positive about life in general, you make yourself instantly more attractive to guys. It doesn't matter how pretty a girl is, if she isn't already happy with her life, you will just spell 'hard to maintain' to a guy. That's no fun. They will be crying 'Next!' in a heartbeat so get happy and show it!
Exude confidence. If there is one thing men tend to agree on it's that confidence is a big turn on! Likewise, lack of confidence is a huge turn off. Many relationships have ended because the girl lacked confidence. This does not mean guys want a girl who is stuck up. They want a girl who isn't making more work for them in defending the girl from themselves when they claim how fat they are or how dumb they act. Stop it! If you mess up, laugh! (see step 1!) This rule also applies to jealousy. Look here, gals, if the guy wants someone else, let him go. You don't want nor need someone who doesn't feel your 'the one'. I've found that being confident in my value as a partner to the point of saying "isn't she beautiful?" when I spot a nice looking woman that my husband thinks it's wonderful, nearly freeing. He can look! A little hot blood in your guy is a terrible thing to squash.
Don't bring up ex-boyfriends once you are in a relationship. Don't dodge the subject if someone else does, but don't ever risk your new love interest feeling he has to compete to 'win you'. Again, that may be more work than he thinks it's worth. After all, he's not in love yet so how does he know how wickedly awesome you are? Be the one who's "easy to love". If you do have occassion to speak about your ex, never talk down about them. This will not put the new guy's mind at ease. It will make him wonder, somewhere in the back of his mind, how much your worth and what kind of trouble may be in store if he sticks with you. Give him the impression that you were just incompatible but you were treated good. The better he feels the ex treated you, the more value he will perceive of you. To beat out the ex as boyfriend material (guys are competitive!) will he need to work harder to be better than the guy who cheated, stole and lied or the guy who treated you like an absolute princess but sadly there just wasn't enough 'spark' to make it last?
Listen. Don't be so eager to talk about yourself. Guys want to be listened to, too. They may not be as prone to exposing their emotions like many women do but they are emotional creatures all the same. They desire being with someone who takes them seriously, who believes in their capabilities and trusts that their interests are worthy of the time they spend on them. With any luck, their new interest will be you!
Look them in the eye when they are talking to you. You are more trustworthy and sincere feeling if you are using eye contact. This goes for anyone you may be speaking to.
Be sincere. Don't fake it just to get their interest up. This isn't a game and guys are not toys. If you don't feel you have the right chemistry, don't pretend. Be kind but be honest. And for God's sake, for better or worse, don't beat around the bush or leave subtle hints. Just say it already! Guys appreciate that.