Here are two special tools that make working with hinges easier. The first photo shows a hinge scoring tool. It actually has chisel like blades on three sides, laid out to exactly the size of a given hinge. You pound it into the wood with a hammer and the hinge mortise is scored on all three sides and to the right depth.
The centering drill shown in the second photo has a little collar that fits into the bevelled part of the hinge screw hole, centering the gadget. Then the pilot drill plunges forward to drill the hole exactly in the centre of the hinge hole.
Both of these can be found at most good hardware stores.