I would recomend bouldering as the best way to improve technique as it is easy to practice moves in isolation and without a real fear of falling. I found the best way to improve technique was (in no particular order):
a) Experiment with foot position (inside edge vs toe tip vs outside edge vs heel, etc), hip position, shoulder position.
b) As a general rule of thumb keep your hips in to the wall and elbows down and try not to crimp every thing. Open handed style is harder at first but you will be less prone to injury and develop stronger, more adaptable grip strength. Tendon injuries take forever to heal.
c) Pick a problem/group of moves and try and do them in as many different ways as possible. See what works best in any given situation.
d) Watch others of similar build to you and see what you can learn (good as well as bad). Watch girls too, as mentioned above women tend to lack the brute strength of many men so often have better technique to compensate.
e) Muscle memory plays an important part and this includes remembering the bad ways of doing things so beware of repeatedly doing the same move incorrectly, once you have a move dialled practice it repeatedly to ingrain it.
f) It is all about balance and centre of gravity. Think a problem through in your head before you do it and imagine the positions you would need to be in, try it and see if you were right.
g) Unless you are on an overhang then most of the support should be coming through your legs, subtle changes in foot position can make all the difference.