It is, pretty much, just a process of trimming, both the branches and the main stem, as well as the roots. This process continues on so that the roots and "plant size" can find an "equilibrium" and make the resulting plant "look" small.
You will probably find it easier to grow in a square or rectanglular pot, because the straight sides make it easier to trim the roots. This way trimming the roots is like removing the crust from a loaf of bread - you just slice a little bit off of the flat edges with a sharp knife! Growing a Bonsai may be the best way to become an expert at repotting!
Just do a Google search for - how to+bonsai. There should be lots of info.
