Okay, grass roots: the roll is the easiest flip-like trick with a quadrocopter. You can do a roll to the left or to the ride side.
Full throttle to gain altitude, then full aileron to the left and throttle down to about 50%. Keep aileron to the left until the quadcopter is in level position again.
At half turn backup throttle again to keep the altitude. Usually you need full throttle for a short time to intercept the flip movement. Altitude is your friend! Find more basic tricks here.
watch on youtube: http://www.youtube.com/watch?v=S4sAJM1uRD0