I just always use a center punch so that it starts in the right place, then make it as square to the stock as possible. I just eyeball it, but they always come out OK. I've done 4 of them, shotguns and lever actions.Need to drill a pilot hole for a sling swivel stud in a brand new shotgun.
I drill the first hole for the screw, then put on a larger bit and just go below the surface to partly bury the wider part a bit. Makes it look cleaner.