Make sure you jump on, don't ride on. Also, straddle the box/rail as you approach it and keep all your weight on your front foot, and as mentioned before, look to the end of the rail, or even past it sometimes so you don't see it at all, because if you look down at the rail/box you will lose balance. You will fall, and when you do, just get back up and do it again it's no biggie, but you will get it. Just spend your day hiking that shit and you will get it, no worries.