Though I play piano, and I've played in an orchestra, I haven't done both together (I played cello in orchestra, not piano) so I can only hypothesize here so bear with me xD
If you get any practice time beforehand with the orchestra before the performance, familiarize yourself with how the conductor does things. While there are "official" ways to count off the tempo and signal decrescendos, crescendos, allegros, ritardandos, and the end of the piece, every conductor has their own quirks. I remember when I played with a different conductor than I was used to, she signaled a decrescendo by lowering her baton almost to waist level and counting off the tempo there, which out of the corner of my eye looked WAY too similar to how my old conductor signaled us to stop playing (waving the baton and then dropping his hands to his side), so me and everyone else who wasn't used to that looked like an idiot when we stopped playing during practice; it happened a few times too xD
Also talk to the conductor if you have the chance, see what modifications they're making to the piece, if any, in terms of dynamics, so you can be ready for it.
Learn your piece well, preferably by heart, so you can look at the conductor without stopping if you need to, make sure you keep him in your peripheral vision too, so you can see when things like crescendos, decrescendos, ritardandos, and accelerandos are coming.