How do I ensure my cooked meat turns out moist?
The way to ensue moist meat is to make sure that you don't overcook it.  It is really just that simple.  Variations on cooking method are to achieve certain effects on the meat, i.e. searing to develop more flavor due to the maillard reaction, sous vide to allow you to cook to a specific temperature, ect.  In the war against dry meat, a thermometer is your best foxhole buddy.

That said, some cooking methods allow you to hit that temp mark easier than others.  Typically, the slower heat enters the food, the closer to the specific temperature you will be able to get.  Thus things like a braise more often result in a meat that is moist as the window between cooked and over-cooked is much larger than on something like a grill.