This is a tip that might sound silly to you now but believe me, you will soon find out why I put this sentence here:
DON'T DRILL IN YOUR FINGERS !
It hurts like hell, makes a mess of your project with all the blood and you will think about your mistake for weeks.
You are in a workshop, full of aluminum dust and particles. The last place where you would want to get a deep cut or hole in your finger.
Always keep those fingers clear of drilling places !
One exception: the main wing spar.
This thing is so damned expensive, and soo many people mess it up by accidentily drilling holes into the spar that this is the place you should put your finger underneath. Replacing a main wing spar because you messed up is just not an option. (pricewise the most expensive part of the whole airplane frame). If you drill in your finger here, you deserved it !
For the rest, keep em out of reach of the drill bit.
