1. Lay down an old Clay Aiken CD, reflective-side up. Position the drill bit in the center hole and line it up with its reflection in the CD for a 90° angle.
2. Make a jig by nailing together a couple of 1×2 or 1×4 scrap pieces to form a right angle. Place it on its side, with the bit pressed flush and tight against the inside corner. Drill down.
3. Spring for a drill guide, which cost as little as $15 and can turn your drill into a drill press. They can also drill at fixed angles.
4. To keep your drill bit from roaming around while drilling, always cross measure and use a center punch to make a dimple in the wood.