I guess you are talking about when playing scales and lead in General? In that case what i do is that i use the baseball-bat style grip on the fretboard and then rest all the weight of my hand on that thumb. This relaxes the other fingers by releasing them from not haveing to actually grip the fretboard and keep it in place. Of course i use a strap and that helps but it can be hell on the shoulders if done for too long. This technique was actually taught to me by my piano teacher funny enough and its helped me.

Its really hard to describe w/o showing you what i mean.