I agree with bownarra. the only advise i would add to this is that i took this advise too literally. I beat myself up about every little thing and it really stunted my bow making growth. I would say, aim for perfection, but know when something is good enough and when its time to move onto the next one.
also, gizmos are great for beginners. I use mine a lot, mostly for initial tiller and as a straight edge. The only thing about gizmos is that they only guide you to a perfectly circular tiller, which is not normally a perfectly balanced tiller. so, for rhyming sake, "A gizmo is a tool, not the rule"