What is the best technique for using a drill to insert screws?
I'm not an authority, but start with this:


Keep the bit inline with the screw's direction of penetration.  Most times I see newbies struggle with that.  If the drill/chuck is cocked in relation to the axis of the screw, it creates all kinds of trouble.
Firmly push inward, not letting the bit slip back out of the screwhead.
Bits are consumable.  They don't last forever.  Are you trying to use a bit that's too worn?  Once a bit has slipped badly even a few times, it's probably toast.
Slower, steady power is your general best bet, the only exception being when you need a BURST of torque, whereby you time your pushing/pressure effort with a burst of speed on the drill.  But that's seldom needed, and you'd still use the low range.