Drill bits are bladed tools, just like knives. While those blades might be tiny, they are still essential to the drill and need to be kept sharp. A dull drill bit makes the drill work harder, wearing out its motor and degrading your investment in a quality power tool. Sharpening drill bits with a file requires nimble fingers, but otherwise is an easy task requiring only a few minutes.
Wipe away any debris, dust or grime that is on the drill bit with a wet rag.
Clamp the drill bit in a table vise. If you don't have one, holding it with a firm grip in your hand will be a bit more awkward, but workable.
Place the file on one of the blades at a 60 degree angle. There are two blades on either side of the bit's point. Use an auger file for a brad-point and auger bit, and a mill file for a spade bit. Run the file down the edge six to eight times. Repeat the same procedure on the other side of the bit.
File off any metal burrs by drawing the file one time up and across the underside of the areas you sharpened in the previous step.
Apply a drop or two of household machine oil and rub it into the drill bit.