Keep it moist!
Moisture is an elusive target with cooking outdoors over dry heat. Meat, when cooked, will cause the muscles contract - thus squeezing out the moisture. The fire will dry up the moisture and help dry it out. There are several ways to help counter this drying process. Consider these steps to add moisture and flavor to your meats:
Try spraying the meat with fruit juices during the cooking process. Try adding a little butter with the juice. Mix well.
If you have a water smoker, you can spray as above and insure you have plenty of liquid in the water pan.
Consider the following: For Poultry, try orange, apple, white graps or cranberry juices.
For Pork, you might consider red wine or cider vinegar.
For Beef, try a beer mixture with water.
Marinade Spray Bottle