To hit a flop shot, you have to maximise clubface loft at impact. For a start, use your must lotted wedge; mine IS a 60 degree. Choke down an inch for control, and play the ball up, just inside your left heel. Don't push your hands in front of the ball at address - you'll deloft the clubface.
The swing should be long and lazy. Hinge your wrists as soon as you start back, creating a 90 angle between the club and your left arm Keep your weight centred. Then swing down, and accelerate through the ball to a full finish.
One move that can kill the flop is an aggressive shift to your front foot on the downswing. This driving action angles the shaft forwards, which reduces loft. Try this drill: Hit flop shots keeping your left heel just off the ground from start to finish. You won't be able to drive forward, so you'll keep more loft on the club.
Annika Sorenstam demonstrating the flop shot...