Moulinets
To execute a moulinet (or actually a half-moulinet) start in high guard (above). Build up power as usual and when it comes to your arm and hand do like this: Move your elbow down and inwards towards your chest. This will make your hand rotate and end with your palm facing up. Your hand will not move much from starting position, but the tip of your blade will move all the way from the top of your shield to the side of your opponents helmet, very fast. If you start from the A-frame guard you will have to make a full moulinet. This is done by more or less going from A-frame to High Guard and then make the half moulinet, only this is done as a single motion. The tip of the sword will move from pointing upwards to almost pointing downwards and then make a half-circle movement to hit the target. While going from A-frame to High Guard you may choose to push your left hip forward. This will make your right hip movement stronger. The most natural movement would make the sword hit with a 45 degree angle, but you can come in more from the side or hit vertically by adjusting with your hand. I really find it hard to put this down in words, so I hope the video will help.
Practice
As with snaps you should do a lot of slow-work, and make sure you deliver the blow with smoothness. Mind your power generation. If anything is strained or hurts you should stop immediately.