I am pretty new to it too, but I would say, don't worry too much about speed if you just started doing it. Of course, go as fast as you can, but I personally wouldn't sacrifice accuracy for speed, that will really muck things up later on. You will get the hang of it the more you do it and you will get faster.
It can definitely get pretty intense sometimes, especially when you have a ridiculous amount to unload, but don't let it faze you. Be sure to always ask other team members if you have any doubts/questions; they will likely be glad to help you. Again, this is just my experience from doing it for a short time recently, but I am scheduled again for it next week. The TLs praised the job I did last time so much, they may want to stick me there now. In general, try to not get too stressed out when they are cattle proding you to go faster... which is easier said than done, I know.