This seems like a no-brainer, but it's a good place to start. "It's very important that you two be able to have a lot of fun together, so a party boy or a screw-up will probably not work out for you," says Mira Kirshenbaum, a family and couples therapist and author of Is He Mr. Right? "No matter how charming he is, if he is still struggling to grow up, it will get very old, very fast."

Picture a delicious platter of grilled steak. Does your man offer it to you first to pick the best piece? He does if he's a keeper! "When it comes to taking the best piece of meat or offering it to you, that's a metaphor for how he'd always put you first the rest of your life," says Rachel Greenwald, author of "Why He Didn't Call You Back: 1,000 Guys Reveal What They Really Thought of You After Your Date."

You know a guy is really into you when he can't stay away, even when you're bedridden and snotty. "When you're sick with the flu, he says, 'Let me come over and take care of you,' rather than, 'Oooh, you sound really contagious... call me when you're feeling better,'" Greenwald says.

He asks about your family, and he seems to genuinely want to hear about them. "Interest in your family shows that he thinks about you as a whole person, and he knows that being with you means understanding and accepting your relatives too," says Sarah Harrison, senior editor of yourtango.com.

In the beginning of your relationship, does your man show an interest in meeting your besties? And does he follow it up with a plan, like hosting a low-key dinner party? "Friends are an important part of your life, and his knowing them makes him more involved with you." Harrison says. "Plus, he'll have to deal with them at some point, so initiating it himself shows maturity."

And she even has a poem:

When your guy calls your mom to tell her about your promotion before you do, that should tell you something. A man who is supportive of you and your goals is typically a guy who doesn't "feel threatened by your success," says Kirshenbaum. "He knows who he is and where he's going," which means he can ultimately be there for you.

Does your man really listen to you? You'll know he's a keeper if you tell him you have a big scary work meeting and the next time you talk, he asks how it went. Or if you tell him you left your sunglasses at his house and he remembers them on your next date. "Following up on things you say to him means he pays attention to you -- always a good sign," Harrison says.

This is the guy who "goes to a chick flick with you on Friday night rather than an action film -- not because he actually wants to, but because it makes you happy," says Greenwald.

A guy who makes you feel like the luckiest woman alive -- like you can (and should!) be your confident, fabulous self -- is worth hanging on to. "It's not just about how you feel about him but more about how he makes you feel about yourself," Kirshenbaum says.