One mistake is unracking the bar with a wide foot position. If you unrack the bar with a wide foot position it makes it very hard for you to perform a good walkout when you unrack the bar... you waste a lot of energy and you also don't involve as many muscles as possible... in contrast, when you unrack the bar with a closer foot position... you involve all of your strength... it's much easier to open up when you walk out.