One of the most important factors in properly sharpening a drill bit is to correctly angle the lead. Typically this angle is 59 degrees. When sharpening a dull bit, you can usually estimate this angle from the existing edge, but if the bit is broken or badly chipped, you'll need a drill tip gauge.
Put on your safety glasses, and turn on the bench grinder. The grinder should be set to low speed.
Hold the drill bit at the shank with your right hand. Hold it between your forefingers and your thumb so that you can rotate it. Hold the bit with your left hand near the tip of the bit so that you can rest this hand on the grinder tool rest.
Point the bit directly at the grind wheel. Move the bottom of the bit to the left approximately one-third of the way to making the bit perpendicular with the wheel. This is a 30-degree move and will set your drill bit lead angle at approximately the correct 59-degree angle.
Apply light pressure against the grinding wheel. Rotate the bit clockwise after you have developed a sharp edge. As you rotate the bit, move the bit to the left approximately 10 degrees to apply the correct clearance.
Check the drill bit to the drill tip gauge. The gauge is designed to show the 59-degree angle as well as having a small ruler to help you ensure equal lengths of both sides of the tip.
The drill bit clearance does not have to be exact at 10 degrees but should fall between 8 and 12 degrees. Take frequent breaks while grinding to check the drill bit and to allow it to cool off so you don't burn your hands. It is a good idea to keep a small cup of water nearby to quench the drill bit regularly.
Always wear safety glasses when grinding as small bits of the drill or wheel can enter the eye. Never wear gloves when using a bench grinder as you risk catching the material with the wheel.