Fly straight and level, about 1/3 throttle (as little as you need to fly straight and level).

Using quick movements, pull all the way back on elevator, and then immediately push both rudder and aileron to the left..... Count to 1. release all sticks so they come back to the middle.

Snaps to the left are normally quicker than to the right....

Depending on your plane, you may have to count to 1 either quickly or slowly...... ;-)

The trick is knowing when to release the sticks, that is what brings you out level and straight again.

Do it with some altitude.....

gus