If you can find one, buy a pin vise.... this is a hand-held chuck, about the size of a fat ballpoint pen, and it takes very small drill bits. When I want to drill a hole in a very precisely located position I measure with a caliper or steel ruler and mark the spot with crossed lines (x mm from the left edge, ymm from the bottom edge, the lines cross at the point I want the hole). Then I use the pin vise to drill a small pilot hole, not very deep, just by spinning the pin vise with my fingers (it takes less than a minute, even in steel). This little hole has the same function as the depression you get from a center punch, but you can locate the hole much more accurately with a pin vise.
Then I drill a small pilot hole (say with a 1/32 or 3/64 inch bit) all the way through, and then drill the actual hole with the actual bit... the final desired diameter.
Lots of fooling around, I know... but I've never drilled a hole in the wrong spot, either. I bought my pin vise at RadioShack.com, but they don't sell it anymore... I tried to buy one for a friend for Christmas, but no cigar.
By the way, a pin vise is absolutely perfect for making a pcb hole a little larger, removing a bit of solder in the hole etc... extremely handy tool.
And all of the advise above about drill bits... yup!!
good luck,
Peter