I have officiated volleyball as well as basketball and softball for 3 years now and I believe the most important thing is to know the rules and know them well, every aspect matters!
A lot of young
vb officials often are reluctant to call the carry, that is, i believe, the hardest call to make. The legal vs. the illegal. it is a carry if there is any prolonged contact, if it comes to rest, or most of the time if 2 hands are used and are not together it is a violation because it is very difficult to simotaneously hit the ball and not have it be a "double hit".
And lastly have confidence in yourself and your calls and have FUN, a wise official once told me that fun is the key and if you aren't having fun, you don't belong officiating, good luck