RULE NUMBER 1, NEVER HOLD YOUR BREATH the reason you don't hold your breath is because the stuff in the tanks make your lungs expand, but if you hold your breath then your lungs will explode. don't go scuba diving alone in case something were to go wrong
always equalize when going down or up.
dont go up too fast while diving deep check your tank every now and then so you know when you are running out of air.