Personally I like to start out early with a very tight range. Almost to the point my 3-bet range in actually my open range, and I'm always shoving. Now if I'm in late or the Blinds, and I am facing a thin open. say 2.5x to 3x. I will call with my typical call open range....
with that said, If I hit I'm shoving on the flop. now after about the 3rd level that's when I switch gears, typically I will have about double my starting stack at this point, and can widen my open range, push people off hands, or call low stacks....
if I'm low stacked, its basic Push/fold range at that point.