Obviously a first class knowledge of the software really helps and speed is a must. I'm too slow at the computer myself which is why I take on assistants. I like them to do all the installations and updates too and have a really good filing and backup policy.
Great assistants anticipate every move and nothing is too much trouble - including humping and setting up gear, fetching coffee, and keeping the studio neat and tidy for the work in hand. And although their cellphones might be on, they don't answer them if we are busy. I respect their talents and hopefully they respect mine.