more careful prechecking definitely.
For music (especially loud music) you need some good isolating headphones and a waveform monitor. Most NLEs have WFMs built in so a laptop works well. In this case the level problem would have been obvious if you had checked the meters on your cam.
You cannot rely on DJ/sound mixers to give you the levels you need. Many times you will get a line-level feed from a board – you can control the levels using pads and the settings on your transmitter and/or XLR adapter.