In terms of fuel, wood is hotter than natural lump charcoal which is hotter than briquets. No matter what fuel you use there are only a few things that affect heat. First is the amount of time the material has been lit. They are all hottest when they have stopped flaming and have a nice ashen gray color. After that they will steadily decrease in temperature. Second is the amount air flowing through the grill. If you are looking for heat, open the vents to their maximum position. Third is the distance from fire to food. This should be a relatively short distance. (Say six inches) Finally is the issue of closing the grill. I really like Steven's advice about anything thiker than a hand having a closed grill.
Now with that out of the way you could be having two problems your food is not browning or your food is not cooking through. If you food is not browning try, 1) Preheating your grill grate, 2) cooking before the coals have cooled (about 20 min after they light) or 3 Try piling up a double layer of coals under the food. If the food is not cooking through you should, 1) let the food come up to room temp. before going on the fire, 2) close the lid 3) don't open the lid.