I love doing shakas! This is my technique for doing them(off a wave).
Approach the wave on a broad reach, with as much speed as possible.
As you reach the wave, bend your knees and start the carve into wind. You should be carving pretty hard as you take off from the lip.
As you take off, lay the sail down as for a shuvit, keep sheeted in hard with the back hand, and lean the upper body forward towards the nose of the board. Do NOT lean back!
In the air, keep the front arm straight and use the back hand to feather the sail and control the rotation.
Keep leaning forward throughout to encourage a nose-first landing.
As you land, keep the front arm extended forward, push the clew through the wind and you're outta there, job done!