I've done my ndsl, phone, friend's psp and my ipod and I've never had troubles, this is how I do it
remove all dirt from the screen
peel off 1/2 of the screen protector, holding the unpeeled side
line it up and make sure you get it on the right spot the first time
apply til half way, with one hand remove the bubbles by using the width of a credit hard
put your hand on the applied side and then peel off the remaining half, BUT LEAVE 1 CM TO HOLD ONTO, apply that and then remove bubbles, apply the rest.