Without a list of your primary prep tasks, like LoneWolf mentioned, advice may be all over the place as far as specific tasks but one thing that used to amaze me were the guys who had no "system" to their prep.
One super-simple thing I do every single time, whether I'm dealing with a lone onion or a sack of them, is to work from left to right. It fits my body mechanics, and allows me to process food from my non-knife hand, onto the board, break it down, and then off the board into whatever container it's destined for (just rake it off the board with my knife into the container, taking advantage of the blade in my right hand).
I also look at what is going to make the biggest mess in my work space and do those things last so that I'm not having to take as much time between tasks to clean my area. For this reason I try to do onions last because the skins tend to stick to everything and require more than just a swipe into the trash to clean my board.