There are a a couple threads where I have posted information on how to hold and how to chord a guitar with reduced fatigue and increased speed--it is really hard to describe these techniques in writing, but part of the secret is to get a proper grip on the neck so that when your fingers hit the strings, the tips are at an angle rather than perpendicular to the fretboard, at little more of your fingerpad touches the string, and you tend more to squeeze and release the string down than to strike and squeeze---