I am in a similar boat as you, having learned some basics and how to keep the trees (mostly) alive but lacking the ability to design the tree. What I've realized is that I don't actually know what a tree looks like, or at least can't really picture it in my mind's eye.
It's similar to a phenomenon I saw on a TV show where the host stopped random people on the street and asked them to draw a working bicycle. Over 90% failed - how the chain, wheels etc. interacted was completely lost on them in their depictions. They drew the basic shape of a bike, but one that would most definitely not work in real life. And such is my understanding of tree structure. I don't live under a rock and have seen plenty of trees in my life, but still can't actually draw out the parts to make a realistic tree. This inability is translating into my bonsai problems.
I've been trying to study different trees as well as bonsai, and have been cataloging the pics I take. I keep progress folders of my trees and will save pics of trees/bonsai into those files as inspiration. I also try to keep folders for different styles. This has worked fine for brooms and formal uprights, but the informal uprights needed further division by trunk shape - "S" shape, bend far down, straight trunk and then bend in the middle, double trunks etc. Shohin got its own folder as the trunks tend to look different than the larger versions to accommodate the small size - I find that the difference between a 28" tree and an 18" tree may be nothing more than proportions, whereas reducing the proportions may not actually work if the tree is too small (depending on species) and then a change in trunk structure is required.
Once I better understand how the parts combine to make up the whole, I can better implement the bonsai procedures I've learned and attempt to create the intended style in the appropriate scale. Until then I will be drawing the proverbial non-working bike even when using the best of bonsai procedure (which I don't always use).
