A few things I do~
Exaggerate a lot. make sure that the hands move extra, and the gun shakes around a good bit.
Remember the weight. holding a gun with one hand, the weight is going to gradually bring the front of the gun down, make sure the animations account for that, having the hand lightly toss the gun's weight a bit to adjust itself.
Change the gun's angle. Animations look cooler when you see the gun pointed a lot of different ways.
Spacing, Spacing, Spacing. this falls under exaggeration's heading. when you ease between motions, and change directions, make a super slow ease, but a super fast weight throw.
that's all I can think of now.
edit- also I added you on msn mickeyb