1. Keep your profile picture simpleTurn your camera 90 degrees to take vertical shot.This way, you'll elimanate all the empty space in the background and don't have to do cropping later.
2.Lighting is ImportantTake your pic in abrightly lit area or under natural sunlight.Avoid dim yellow lights as the photo will either end up too dark or if you use flash,you might look washed out.
3.Avoid looking delibrateThe best dp are those of you looking the most natural and not intentionally dressed up to take it.Relax and smile :D And steer clear of lingerie and drunken shots as you never know who might be poking around in your Facebook,blog or other social networking!
Thats reality especially for the gurlssss ( including me too .. Hahaha :P
And duckface bagai - .. -''
Image from google courtesy ^^,