No special technique really. Just make sure to have the drill as vertical as possible and to press down smoothly. It should take only a few seconds to cut through and leaves a fairly clean hole. However, for my 3" diameter tower I only drilled a 2.25" hole.
Primary: Apfelwein, Raspberry Lambic, Experimental Wheat cider, IPA
Keg 1: Hefe
Keg 2: Irish Stout
Keg 3: Peach Kolsch
Keg 4: Empty
Bottled: Bourbon Vanilla Porter, Chocolate Stout