Does anyone know of any guitar coordination exercies, mainly for your fretting hand?

I've played guitar on and off for about 3 years and I've only just started to get back into it now that I've got some spare time. Unfortunately I feel I've lost alot of my muscles in my left hand. I can play some alright metal, eg. opening to Ants of the Sky-Between the Buried and Me but I feel really unco in doing so and i can't really coordinate it. My pinky finger always locks up too. Any tips?