Routine avoids mistakes.  Think about your pre and post dive routine. Don't have one? Then create one.  Whether it is a mental checklist or written out, if you do it the same way every time then it gets easier and you avoid mistakes.  An example for me is my mask box contains more than a mask. My defog, earplugs, Earshield drops, and mask cleaner. Take the mask out and put my watch and sunglasses in. I always know where my stuff is and never forget my earplugs or defog.  After the dive, my wrist computer goes into the box and my watch comes out. All parts and pieces go back where they are every time and I have less to remember. I rinse them all in the box and life is simpler.