1. Learn people's names.
Not just the director, choreographer and musical director. Learn the names of the rehearsal pianist, the the production manager, the spot op, the sound team. Those people work really hard to make sure you look good, and to get butts in the seats. Most likely they are also fabulous people who will give you a break from cast drama. And one day they may very well be asked for a reference about you. You don't have to befriend them excessively or kiss up at parties. But do your best to retain as many names as possible. Then they're more likely to remember yours.
2. Return from breaks on time.
If you're working a union contract, you'll be given a five minute break every hour, and a ten-minute break every hour and a half. While I'm sure you know to be on time for rehearsals and performances, you should also be back on time when breaks end. Yes, the stage manager will make an announcement. But he or she will also have given you a return time, and you need to honor that. Wear a watch. Set an alarm on your phone. Do what you have to do. Just make sure no one has to look for you. That holds true for tech as well.
3. Be Off Book by the Second Rehearsal
When you start a contract, you want to be very, very familiar with your part. But you do not need to be memorized. In fact, you want to have your book in hand so that you can write down your blocking. Nothing is more annoying than an actor who insists that he's memorized the first day, doesn't write anything down, invariably stumbles through his lines, and retains none of it. Then we have to go over it all the next day. Amateur.
Once you've been given something, be it your blocking or the tenor line, you're expected to know it the next time it's rehearsed. No one has time to review, nor should they have to. This may mean that after an eight-hour rehearsal day, you have extra work to do at home. Suck it up. Show business is hard.
However, that also frees you from the expectation of perfection. Rehearsal is exactly that: rehearsal. You can stumble and fall, experiment and fail. Having a hard time picking up a tap combo? Assure them you'll have it by tomorrow. Then record it, drill it, sleep on it. Impress the socks off the creative team. We can't always be perfect. We can be reliable.