Great points made above, a couple more:
DO use an arming plug to isolate the main battery(ies).
DO measure the load on your system when you fit a new component so as not overload.
DO warm your batteries when they are cold ie. get them to at least 20 deg c (70 deg f)
DO check your batteries before EVERY flight.
DON'T fly if the sound from the motor changes - there IS something wrong
DON'T discharge below 20% remaining capacity

These are all lessons learnt by me or my friends the hard way!