First, you need a design. Start by looking at the tree and ignoring all the foliage. You will see the "bones" of the structure. The most important part of the bones is the base of the trunk and the trunk line. Then in priority order come the main branches. The secondary branches can be ignored for the purposes of your design at this time.
What you want to do is look at your structure and decide where you want to take your tree. If you are drawing a blank, go online and look at other procombens bonsai, and find a photo that looks similar to your tree, but more finished. Or for that matter go online and see if you can find trees in the wild that inspire you that you want your bonsai to look like.
Once you have your design figured out, it becomes a question of pruning, wiring and shaping the tree so that it fits your design. Sounds simple, but it can be if you have decent reference material.