Some things to keep in mind…collected from wise people around the net:
Brent Wilson….My Guru! Link: http://bonsainurseryman.typepad.com/bonsainurseryman/2006/10/
FIND WHERE THE TREE STOPS BEING INTERESTING. This rule applies to advanced and promising material that hasn’t been completely styled. Usually a suitable candidate for this rule disturbs you in some way. You get the feeling that this should be a good tree, but there is just something wrong that keeps it from being really great. The trick is to start at the nebari (as usual) and go up the trunk inspecting each element. Where the tree stops being interesting is the problem. More often than not, it is a long straight portion of the trunk that is boring, but it can be anything that is ugly or out of character with the rest of the tree.
AVOID THE DREADED “C” CURVE. A powerful concept in bonsai design is FLOW. This is the idea that there is a visual energy flowing through the tree. It can be tickled and diverted, but it always comes back to the same direction (except when you want dynamic tension). But flow should not be stopped in its trip up from the nebari and out through the apex. Of course a tree can several bends in the trunk that slightly change the direction of the flow. This is what we call MOVEMENT, and even the term alludes to flow. There are several things that can stop flow, but one of the most overlooked is a “C” curve in the trunkline. A bend in the trunk will stop being aesthetic when it starts to close, as in the ends of the “C”. Instead of the eye dancing around the curve and up the trunk, the visual energy will stop or shoot out of the trunkline rather than moving up to the apex if the bend is closed. This is a very subtle but powerful concept.
WORK WITH WHAT THE TREE SHOWS YOU. This is another rule that you think would be obvious, but many people don’t think in these terms. Instead of being partners with the tree, they try to bend it to their will. I don’t consider material to be pre bonsai until it shows me something. Once it does this, then I prune and work with the tree to enhance what it has to offer. In fact, I find many trees are completely built around one excellent feature. Usually it is the trunk, but can just be the bark, or a uro, jin, shari, or the nebari. Something about the tree that is truly excellent. On many trees with outstanding trunks, the branches and foliage are just window dressing. In fact, you want to design the tree so as to enhance the outstanding feature, not to detract from or hide it. This is related to trying to see the tree in the tree. The essence of thetree will often be one outstanding feature, and the rest of the design will be obvious once you see it from this point of view.
More to be added later