Someone please correct this if I’m wrong, but I do also recall Tom Silva echoing this once:

There are standard rules and methods you should observe.

1. NEVER drill a hole within 1’ of the end of any beam or a floor joist. You should also avoid drilling within 1’ of where a beam sits on top of a support column or post.
2. In overhead spans, the 1/3 1/3 rule generally applies. Only drill within the 1/3 middle of the span horizontally and the 1/3 middle vertically.
3. Never drill holes of the same size next to each other. Vary the vertical location of holes. This includes existing holes.
4. Drilling several smaller holes at varying elevations on the beam is better than 1 large hole.

http://www.techresource.online/training/ssnw/drilling-beams