How NOT to use a power drill. What are common mistakes that should be avoided?
Some other helpful hints (not from Heloise)

0) ALWAYS wear gloves and eye protection. (Note: if you're using one hand to hold down the material being drilled, a glove can reduce injury if the drill bit jams. On the other hand, you should never depend on body parts to hold things in place)

1) When drilling into soft material such as plastic or pine, withdraw the bit periodically to clear out shavings.

2) When drilling into metal or hard materials, use a center punch to give you a starting hole. This avoids "wander" when you start up, and reduces the need to push down hard in an attempt to avoid "wander."

3) Don't put a gigantic size bit (e.g. spade or Forstner types) in a drill not designed for one. The torque required will burn out the motor. 

4) Not bad for the drill, but bad for the bits: when using really small diameter bits, be careful and gentle or they'll snap.  If you've got a 3-prong chuck, make sure the drill bit is properly centered before attempting to drill.

Note: it's fine to drill at an angle so long as the applied force is along the shaft of the drill bit.