When you are setting up your profile, think about how people will see you in your photo, as generally that will be the first thing they look at, and if it isn't appealing, you will no doubt get passed by however good your description of yourself is.
So make sure:
1. Its in focus.
2. Its nice and light.
3. You're smiling!
4. It's reasonably close up.
5. It's not from a drunken night out.
Follow these simple rules and you'll be one step ahead of about 60% of the competition!