I do it the way DP's book says. Take a 45 degree up line and roll (left) to a right rudder climbing KE. Snap with full right rudder, full up elevator, full right aileron. After 1 and 1/2 (or so) snaps, move the right stick from the bottom right corner immediately to the upper left corner. Hold that with 3/4 to full power. If you have the coordination to do so, click in 3D rates just a half second after the right stick switches position.

The first snap and a half is to get the plane "wound up", and lose it's airspeed rapidly. After a few tumbles, the plane will fall into a nice inverted flat spin.