Go to the Valley Cushion thread on the Pines forum and read it from beginning to end, there's a lot of good information there that will be useful to you.
As to this tree. If this tree is going to be viewed as Pre-Bonsai it is up to you to bring it to that point. In my opinion you are going to have to treat this tree as prue raw stock and make it grow into what you would like it to be. This tree is probably not much older than five years if that and it demonstrates a lot of the problems you will encounter with young Mugo Pines. First of all the trunk is nothing to jump up and down about. Secondly the branching is nothing to jump up and down about. Those are the two major thing you need to contend with.
What you need to do is decide that the tree cannot at this point be styled into a bonsai that in five years you are going to be happy with, you need to treat it as a seedling or potted liner. One of the flaws in Mugos is the tendency to form knuckles. This one is not too bad but it is bad enough. What I mean by knuckles is a large bulge at the area where a group of branches have emerged from the early spring growth. This is common in most Pine but annoyingly so in Mugos. If you look you will see the the trunk where the first branch emerges is larger than the trunk below it. This will cause what we call a reverse taper.
I recommend removing that lower branch, but leave a one inch stub, do not cut it flush to the trunk. Proceeding up the tree you will notice a similar knuckle formation in every spot where you have branches. These are not too bad and can be dealt with. I suggest removing all but one of the branches at each location, generally the largest, leaving stubs as before. By doing this you will stimulate back budding on the trunk with a tree as young as this one. Place it in a larger pot or pond basket and let it grow being careful to not disturb any of the new buds that will break on the bare wood, these are very fragile and easily damaged. The more of these new buds you can get to develop the more options you will have in the future to remove branches that are too large for the trunk. Planting it in a larger pot or pond basket will allow the trunk to thicken. Your goal is to get the trunk to thicken instead of the branches which is the tendency for young Mugos.
This process is going to take some time but by the time the tree starts showing signs that give you ideas for a bonsai you will have gathered the developmental skills to work with larger trees and older trees.