Good thread.
Here's a short list of
things to avoid:
- getting in the water without knowing how much gas you need at a minimum, for the depth you are planning to dive to.
- using your hands
- getting complacent about skills (not practicing air shares)
- skipping predive planing
- touching the bottom with a finger or fin to stay in place
- Not checking on your buddies remaining gas when you check yours
- diving deeper 'just because'
- straying from your buddy (ask yourself: how far could I get if the next breath I took from the tank simply wasn't there?)
- letting you light 'drop and spin' for night dives when needing your hands. Looks like you're signalling that you are distressed.
- not testing your backup gear before getting in the water (reg, lights etc)
That's it off the top of my head, there are probably many more