Its hard to tell what more you can do (not much to begin with). Also, a side angle photo might help. If you are happy with the size and simpleness of the tree then let it grow and start to refine the branching. Its hard to turn something like this into a really nice bonsai unless it is planted in the ground and left for many years.
its a difference of buying or collecting trees like thishttp://www.bonsaiboy.com/catalog/junipers.html
Everyone has to start somewhere, i am still at the beginning. Its better to learn on small cheap trees. My first trees have tough me a lot, and those trees are 'no longer with us' ;) I am beginning to feel more and more confident using larger and nicer material.
A year or 2 I thought i understood how patient I had to be with older (and especially recently collected) trees. I was wrong, my experiences continually show me that i need to be more patient.