There are plenty of times when a Saturday mechanic must drill a hole in some part of his car. Done right, it's a simple job; wrong, it can give you a headache.
To drill a hole correctly, you have to do two things: use a center punch and drill at a straight angle.
A center punch has a sharp point at one end. You place the point against the metal to be drilled exactly where you want the hole to be and hit the punch with a hammer. The sharp point makes a small dent in the metal. Put the drill bit's point right in the dent, so the bit won't wander.
This is especially useful when, say, installing an accessory mirror on the door. Suppose it takes three holes - obviously they have to be drilled at the exact location or the screws won't align.
Before striking that first blow with the hammer, make an "X" where you want to drill the hole. Place the point of the center punch where the two lines of the "X" intersect hold the punch firmly against the metal at a right angle to the surface. If you hold it at a slant, it may slip.
Hit the punch only once, remove it and make sure the indentation is where you want it. If it needs to be deeper, set the tip of the punch in the indentation and hit it again, once. The force of the blow will cause the punch to bounce out of the indentation, and if you strike it again without checking you'll end up with another indentation you don't want.
When drilling, keep the drill bit at a 90-degree angle to the metal. Holding the drill at even a slight slant can cause to slip out of the indentation.
If you have a variable-speed drill, it's best to depress the trigger just enough for low rpm until the drill bit bites out enough metal to center itself. If you turn the drill on full speed immediately the bit may jump out of the indentation. Once the drill bit has centered itself, run the drill at full speed until the bit has drilled through the metal.