Advice for judging a limited PPTQ during release week
1. Watch a TON of Magic. If you're not otherwise occupied with deck checks or another call, always be aware of games going on. You might see an infraction you need to step in on; you might see a clever play that's legal but you'd never considered before.
2. Competitive is competitive. You've played in a bunch, so you've seen how those judges have handled situations. The biggest thing when making the transition from regular to competitive is that things are much more strict. Regular is largely “eh, do what makes the most sense.” Competitive has much less leeway involved. The IPG is pretty clear-cut for most situations you're going to run into.
3. Set a goal, and try to meet that goal. It doesn't matter what it is. Maybe it's “get my deck check time down a little because the last event I was kinda slow.” Maybe it's “have better table manner than the last event I worked.” It doesn't matter what it is, but try to identify something, whether that's something you've noticed in yourself already or just a general “I've never done this before, let me make it a focal,” and make that your target for the day.
4. Don't be set in your ways. This applies more for when you're working away from your home store, but not everybody does everything the same way. Is the shop doing something differently or not doing something you're used to? Roll with it, get a feel for how it plays into the event. If you feel your “known” way is better, bring it up! If you realize their way is better for one reason or another, cool! Internalize it and bring it back to other shops, so everybody can benefit.
5. If you make a mistake, that's okay, but own it. Maybe it hasn't come up before for you. Maybe you give a ruling that is just flat-out wrong, but it doesn't get appealed, and then it affects the outcome of the match. These things happen, to everybody. Confirm the right ruling with some other resource, relay it to the players (preferably when the game is over, since during the game is only gonna exacerbate the feel-bad of the situation), and end it there. Don't hate yourself for it (lord knows I did) – mistakes are human, and, for the time being, we have not yet been replaced by judgebots.
6. Have fun. A happy judge is a good judge.