Compose with the front, focus with the back works for me. I don't use a lot of light, but I keep a pretty good amount of dark material around my head and the ground glass to maximize what is available. Make sure you close off the bottom as well since that lets in more than you might think (grip together with a free hand, use some sort of elastic enclosure, etc.). A set of reading glasses help, if you don't already use them, to get closer to the ground glass. I normally work in the 12:1 (12x) range, but go up beyond 20:1 when the subject calls for it. Don't forget to compensate for bellows extension.

Of course the biggest suggestion is to practice.