Use R2 to move slightly away from the ball so it drops at your feet rather than your head. It's pretty hard to judge it, but if you play lofted balls using R2 it gives you a little bit more time to line it up.
Also try and leave pressing shoot until quite late, or they will attempt the head. Wait until after the ball has drop passed head height before pressing shoot. you don't always have to get alot of power bar onto the shot for it to sail into the goal at a fast pace, so dont worry about holding it down for too long. Best time to volley is JUST as the ball hits the ground, if not a split second before hand.
As for someone saying press L1, i dont think thats true atall, that just changes player.
I just posted this volley up on the site, shows a bouncing ball being smashed on a side volley from Pavol Nedved.
http://media.putfile.com/Nedved-Volley-on-PES5
And for things like scissor kicks i find it best to double tap half a second before the ball reaches you. I dont know if thats the definitive method of doing them, but it seems to do them when i want to do them.
