1. As a general rule, you should make sure your work is clamped down securely. Having a piece of metal or wood pop out and the drill bit puncturing in to your leg would not be a pleasant time.
2. Don’t wear long sleeves or loose clothing when drilling. If you are using a 24v cordless drill, a single piece of clothing caught in the drill bit will wind up clothing extremely quickly.
3. Don’t force the electric drill to drill. Instead, let the machine do its job. This goes for other tools as well.
4. You should always start off very slow and work up to a faster speed. Starting off quickly is only going to have the drill bit dance around and end up elsewhere.