Heron's Bonsai on YouTube has a few videos, e.g. [1], where he prunes garden trees and describes his thinking. There are just a few principles to learn: cut to discourage growth in a given direction and encourage growth in the other direction, remove growth that grows inwards and/or upwards, remove branches growing towards other branches, thin out growth to create visual separation between branches and to make the trunk and branch structure shine.
After watching three or four videos, I felt confident enough to try my hand on some small trees. It's quite satisfying. The process is pleasantly engaging and relaxing once you push past the natural anxiety around cutting off a tree's limbs, and even a complete amateur can dramatically improve the appearance of a tree in a couple hours.
Gardener's World has been giving arboreal advice for decades in the UK on mainstream TV, along with what to stuff in your herbaceous borders.
I also have rather more than a passing interest in bonsai (for 30+ years). You can't wire a full sized tree as you might with bonsai. Nor can you pinch growth in pines as you do in bonsai. Jins and saris etc would be butchery in full sized trees - to be honest I'm not keen on them in bonsai.
When it comes to full sized trees, look a little closer. Notice all the insects, tiny mammals (if you can spot them), fungi etc. Trees become an environment of their own within the larger environment.
There is nothing wrong with turning an environment into sculpture. At least you care about it! However, I recommend that you do not use bonsai rules to guide your full sized tree management.
After watching three or four videos, I felt confident enough to try my hand on some small trees. It's quite satisfying. The process is pleasantly engaging and relaxing once you push past the natural anxiety around cutting off a tree's limbs, and even a complete amateur can dramatically improve the appearance of a tree in a couple hours.
1. https://youtu.be/sIE882Lx1NQ