Forget POF. Nothing but crazy wishy-washies who are waiting for a Brad Pitt look-a-like (no less will do) no matter how average they may be themselves.
But if you are going to try, good luck. Think of funny things to say, make them smile. Make sure your pics look good or all you'll get messages from will be "heffers."
Make your profile stand out. Say funny things and sound confident. Tell them what you are doing with your life and what you do for fun.
When you message them, don't say too much. Invite them to read your profile, make a comment about theirs, say something witty, and let that stand on it's own. Let them make the next move. Don't send a second message, ever. Move on.
Be careful too, lots of these girls are friends, and if you are piling up inboxes in your local area you may come across as a jerk. I messaged a girl and her sister (unbeknownst) at one point and got in a bind with both.
I no longer use that site, but that's my preference. Just didn't seem that anyone other than "big" girls were very serious. I'm using eHarmony just to see how it goes. I figure if you pay, you are bound to take it more seriously.
One last thing, don't use that site as a crutch. At one point I was not going out much. Put yourself out there and work on meeting people the old fashioned way. Don't log in every day because that site shows it to them. Thats a tough thing to do if you have a lot of spare time LOL.