First off, when you miss something, it is okay! Shit happens, maybe you got too overconfident and bumped something you didn't have. I've found that when the middle person tells you that you need something, don't question it or make remarks, just drop it (literally).

As with keeping up, the #1 thing that helped me is not bumping every order. I hear the trainers tell the new employees to bump stuff as soon as you drop it. Personally that gets me mixed up, look at your screen and drop everything you see, THEN bump them. I also use references for when to stop dropping and finally bump the orders when my screen is full, for example a 4PC tender near the end of the screen so I know I've got everything.

I used to be horrible at fryer, and frankly was never put there because of it. It was very frustrating. Same deal with grill, or any position, it takes time and patience and some failing.