Wrenching practices to avoid...

[egnorant]

Worked with an old mechanic when I was about 10 or 11 and he was full of wisdom.
Did mostly tune-ups, oil changes with a few starters, belts and general car repair.

If you gotta grunt, you might be using the wrong tool.
Engine bay is not tool or parts storage, use the damn cart!!
Tools put up before the hood goes down.

 

[harrytbagger]

Be careful that your wrench doesn't slip off of a bolt that is stuck, this may happen.

 

[zakmartin]

Always unplug your power tools when you're changing out blades, drill bits, wire brushes, etc. It's so easy to hit the trigger at just the wrong time.

 

[slob]

Don't wear gloves while using things with rolling pinch points.