Tim H's comment is a good place to start, since doing two different things with two hands at the same time is pretty much the same process on every instrument.
Some general advice for any instrument:
- There are no shortcuts. Patient, consistent practice is always the most important part of learning any skill, and certainly musical instruments.
- The more difficult the part or technique, the slower the tempo should be when you start practicing it. Only speed up gradually when you have it down cold at a slow tempo. If you keep struggling, slow it down even more.
- Practice each hand separately until you can play each part without concentrating on it, then practice both hands together. You probably will have to slow it down again when you combine both hands until you get the hang of it. You may have to get at least one hand to the point where it can play its part automatically so you can focus on the other hand, if the timing is very complicated.
Specific to pad controllers:
- Most of the time you can use more than one finger on a hand to hit two pads at the same time. The easiest but least flexible approach is to assign each pad to a finger on a hand, and that hand and finger strikes the pad when the pad should be struck. A more flexible approach that would require more practice is to have multiple fingers on one hand playing simultaneous hits on one to three pads, only paying attention to what should be played simultaneously, and hitting some pads with one hand sometimes and with the other hand at other times.
An example of that last: Suppose you have a hi-hat pad you want to play with your right hand of just eighth notes, a kick pad you want to play with your left in quarter notes, and a snare part that is syncopated and sometimes plays on the eighths. You might want to hit the snare with your right hand the same time you hit the hi-hat at some points in the beat but use your left for other snare hits when you're not hitting the kick.
Getting a pattern down of which finger plays which pad when can be complicated and time-consuming, but for the most complicated parts you will almost certainly have to spend the time to figure out the optimum fingering. Once you have figured out a fingering that seems to work, don't change it. Practice it until you get it down or until you decide that it definitely is not going to work well. Then make minor changes and stick with those as long as possible. If you keep changing your fingering you'll never get the muscle memory you need to play the part.
