Certified GKH Gardening Expert
Bonsai trimming is more of an art than a skill or a set of instructions. Part of the art of bonsai is contemplating the shape and form of the tree and envisioning the shape and form you wish it to eventually take. For this reason, it would be difficult to give you an exact answer as to how to do this.
That being said, this article has some tips on when and how it is best to trim your bonsais: