I have had (and still wrestle with) peroneal tendinitis. Strengthening your stability muscles (proprioception exercises like standing on one foot with your eyes closed, using a dyna-disk or other stability disk) and stretching your calf muscle will help. It also seems to help me to self-massage high on my calf on the outside, under my knee - where the top of the peroneal tendon attaches. Good luck getting rid of it.