Here is a good simple exercise that is designed to force your mind to use the fingers on the left hand independent of themselves. This is meant to be done on a table or a flat surface, but it can also be done on the guitar or just in the air as well. The idea is that you should not exert any energy or feel tension in your hands (although you probably will). The idea is to force your mind to casually lift the fingers, and not the other way around where your fingers are trying to force the mind.

Lay your hand on a flat surface and slightly arch your fingers...



Now raise just your index and ring fingers...



Put them down and raise your middle and pinky fingers...



Remember to try to keep the battle in your head and not in your hand, this is a really simple exercise but it really helps with speed and dexterity.