As far as drawing a transmutation circle goes: If you notice, it seems like everyone has their own specific circles that they use, even if they all come from the same base. Just keep in mind the idea of circulation of power, where you want that power to go, what you want to do with it, and you should be ok... like in Mustang's glove, one side of the equilibrium is heavier than the other. That's cuz he uses the glove to generate sparks--positive energy output--and then manipulates them into fire. On the transmuted trees (i can't remember the names, but the brothers posing as Ed and Al), the younger one's circle uses lines that make the bottom heavier. Tree roots are manifested below (hmm, there goes that up-down thing again), because the energy is directed outwards.
Don't get me wrong, i don't think it works or anything like that... but using the basic ideas of balanced geometry and this power flow technique, it's possible to make a pretty sweet-looking circle. I've done one in photoshop for a whim, it came out rather good methinks.