When I did some searching on breathing about a year ago I read about alternating which foot you exhale on. When you contract your diaphragm with the rest of your body consistantly hitting the same position (right or left foot) it can gradually push blood. I read that it was best to take an odd number of steps per full breath cycle (inhale+exhale). I do 4 steps on the inhale, 3 steps on the exhale. So: inhale(L) exhale(L) inhale(R) exhale(R). Supposedly this cuts back on cramps, and I can say I certainly noticed a difference. I have no proof that the breathing was what did it, but I don't think it hurt.
edit: I should add that I found the 4/3 to be nearly impossible to maintain on hills, so I'll sometimes drop to a 3/2, even if only for a few breaths.