My biggest mistake? More like my biggest mistakeS... First off, putting my stand too far away from the action. Take the time to scout trails that are hot and be ready to move your stand frequently.. if you have to (sometimes you don't). Secondly, movement in the stand. Since you are close to the action, you have to be on full alert. Things can happen FAST. Think about every move you make and if you truly need to make it. Also, don't get caught in an awkward position in your stand. I laid one of my legs up on the seat on a 2 person stand this past fall and it cost me a nice buck, because I was stuck, and couldn't move to get in position. Thirdly, don't forget your release. Fourth, be able to judge your distances. When you are sitting their waiting, that's the time to be thinking about which pin you'll use for each shot. Fifth, it's always easiest to draw/shoot standing up, but it can be done sitting down. Practice both and see which feels more comfortable. Sixth, DON'T FORGET YOUR RELEASE!
...and on that day when my strength is failing, the end draws near and my times has come, still my soul will sing Your praise unending, ten thousand years and then forevermore!