Some great advice here. I would add another tactic for riding trees which is very simliar to riding gates. A lot of people tend to wait till they get above the tree to turn this typically causes a person to be late and have to make more gross movements to get the board to swing a round and turn. It also doesn't allow them to focus on the next turn and line of turns they will need to navigate the trees. The next to you are in the trees try to thing about finishing your turn on the downhill side of a tree each time. It should allow you more time to complete turns in the tree and pick your line.
P.S. There will be spots in the trees where turning is not in the cards and picking a straighter line is more appropriate. In general though in a well gladed run and even in sections of gnarly tight helmet branch breaking trees that the above tactic will work.