I should have also mentioned that there are 2 basic methods of cooking, moist heat, and dry heat. Moist heat methods would include steaming, poaching, cooking in crock pot etc. The thing you need to remember about moist heat cooking, its that you want to save any liquid you're using to cook the food in, as it ends up being nutritious having absorbed some of the water soluble vitamins and minerals in whatever you're cooking. The benefit to moist heat cooking is that you end up with a moist, tender finished product.
Dry heat cooking would include roasting, broiling, pan searing, grilling, etc. This can be more difficult for some people, and is usually why people end up with a dry finished product. Some of the problems with grilling a chicken breast for example, it that it's fairly uneven, the edges will cook faster, and be dryer than the middle of the breast, especially if it's thick. You can butterfly the breast to make the thickness a little more even, or cut it into strips, it's up to you. An alternative is to use dark meat (legs and thighs). Not only does dark meat actually have waaaaay more flavor (chicken breast tastes like pretty much nothing), but it's virtually impossible to dry out dark meat.
I should also add that it's a complete myth that searing meat seals in juices. It's been a long standing urban legend in the kitchen, and it's been scientifically proven that searing meat actually results in a slightly dryer end product. I hope this helps, if you have any questions, feel free to ask, I will be happy to help