There are four different ways of doing the propeller. Clockwise and counter-clockwise with both the right and left hands. I have the opinion it is easier to learn the propeller doing it clockwise for right handed people, and counter-clockwise for left handed people. My reasoning probably comes from my juggling background where the first thing taught is the cascade. In the cascade the hand motions are clockwise for the right hand and counter-clockwise for the left hand. So it just seems natural to me to do the propeller in the same way. Having said that, I think doing it in either direction is fine, and you should actually learn how to do the propeller in each hand, both directions.
A couple variations to the propeller is doing a propeller with your arm under your leg, or behind your back. Then try to change between positions by tossing the devilstick in the air, switching arm position, and continue without stopping the propeller.
The picture is of a propeller spin behind the back. The left handstick is high in the air to get it out of the way (it also looks a lot cooler :).