Just as it applies to almost any skill set in golf, repetition is the predecessor of confidence. You have to learn to feel creative shots over and over in order to gain a confidence for hitting them. For example, I spend hours around the chipping green hitting the most ridiculous shots you could ever imagine. Plugged lies, flop shots, balls resting up against the collar, etc etc. If you hit these shots over and over you will gain, at the very least, a little bit of feel and thus add a bit of confidence when trying to hit these shots.
When it comes to the trees, it is relatively obvious that ninety percent of the battle is assessing your options and choosing the best shot for that scenario. And the only thing I would really mention from there is to avoid "forcing shots". For example, a player who plays a natural thirty yard draw has little to no business trying to hit a giant fade or something to that extent. My thought process in a scrambling situation in the trees goes a little something like this:
-Do I have a good chance at getting on or to a safe point around the green? and if not...
-Do I have a good chance of getting it to fifty yards? and if not...
-Do I have a good chance to get it to 100, 150, etc., and if not...
-Can i get the ball back into the fairway or give myself and open next shot? and if not...
-Is it smart to try to hit this ball or should i take an unplayable and drop in a better spot?
This tends to be a fairly consistent way to assess your options in the jungle