Don't Let Go of Your Board
Invest in a good leash and check it before hitting the water.
Broken leashes happen, but do your best to keep control of your board.
Learn to duck dive and don't let go of your board. If you are longboarding learn to turtle roll. There could be someone behind you and getting hit by a board is no fun.
Letting go of your board is a bad habit, it puts a lot of pressure on your leash and it will eventually break leaving you stranded and have to swim to shore.