It's best to let your plants get established before you do any severe pruning.
I have a few shrubs that I pruned into tree form, you have to keep a main stem that is sturdy and straight and cut away any competing branches, any suckers or any crossed or rubbing branches as well.
I pinch away any tiny little branches I see
growing where I don't want them. It'll all take time and a little trial and error.
Hope this helps some, if not just ask some more.