Get as many cues written into your part as possible so that you won’t be worried about your entrances. Mark where the phrases begin, because many times, the rehearsal numbers are not where the phrases are! For example, if there are eight bars to count, but the phrase begins in the second bar, mark 1/7 in the 8-bar phrase. Listen to the recordings if you can get them. If you are still worried about entrances, ask the conductor to cue you. Get there early enough to tune and warm up, and tune to the A that the orchestra plays. It may be sharp. Get an electronic tuner and microphone, if you don’t already have one. When you are in the orchestra, listen to what’s going on around you and try to blend in with the others. If something sounds wrong, it could be you, so it’s better to leave out some notes than to play dissonances. If they are playing faster than you can keep up, have a Plan B. Practice a simplified version of any really hard parts just in case the orchestra gets adrenalin-happy and starts galloping. Find out where the most exposed places are and practice those the most. Remember to stay loose, keep breathing, and have fun!