Find a mogul run that is not too steep and where there is roughly the same distance between each mogul. If no such slope is available a normal mogul run can also be used.
The only thing you really need to master on a mogul run is the bending and stretching of your knees. Start by focusing only on the bending motions. Traverse the slopes and evert time you hit a mogul, bend your knees. You must actively absorb the mogul beneath you. Imagine that your legs are working in the same way as a shock absorber on a car; every time you come across a mogul, the shock absorber gives way to the pressure of the bump. Keep your upper body as still as possible and let all movements come from your legs. Keep your arms well in front of you so as to support your balance.
Bend your knees when you hit the mogul. Extend your knees after the mogul.
When you are getting the feel for the absorbing motion, change your focus. Stretch your legs in the troughs between the moguls. The aim is to be able to traverse a slope and to be able to "even out the pressure". If your legs give in to the pressure when you hit a mogul, and then stretch out again when you have skied over it, you have eliminated the mogul! Try to ensure that your skies have contact with the snow at all times; the moguls should not be small ramps where your skis catch air. You need to "absorb" the mogul in the right way by working only with your legs. Bend your legs by pulling them up under you and not by bending your body towards the skis.