Cool.
Before the show:
1) Remember your ticket. If you're picking it up at the box office before the show, I suggest to go during lottery times so one and a half hour to two hours before the show. If you go after lottery, it'll be packed and if you go when the box office just opens, it'll also be packed. There's usually a lull during lottery since everyone else is outside doing lottery.
2) Check your seat location. If you're in the balcony, remember that there's a long winding staircase ahead of you. So if you have a hard time traveling stairs, you might want to get there closer to when the doors open not closer to when the show begins. If you're in the mezz, it's not a too far a trek. If you're in the middle of the row, don't arrive a minute or two before curtain because you don't want to bother too many people coming in.
3) There is a coat check where you can drop off your coat or large bag if you need to. If you're short (like me), you can borrow a cushion or pillow to sit on. The bar is open with drinks and food which you can take into the theater. The merchandise table is also open. The restrooms are downstairs for your use, too. There's no intermission so I suggest you visit beforehand.
4) Turn off or silent all cell phones or anything with a noise.
5) Flip through the Playbill beforehand if you want. I sometimes find it annoying/distracting when the person next to me is flipping through the Playbill during the show to see who's singing what.
During the show:
1) Just sit back and enjoy the show.
2) No video, photo taking allowed. Try to keep talking at a minimum.
3) Please stay throughout the entire show, even "Good Riddance."
After the show:
1) Most people exit through the side doors to the street. However, you can still go through the main doors to the lobby. So, if you want to go to the restroom or buy something from the merchandise table. The bar would be already closed.
2) The barricades will probably be up. People would already be outside waiting. So, you can either wait around there or leave.
3) A handful of the cast usually comes out to sign through the main stage door. The rest come out the glass doors. When they come out the glass doors, it means that they aren't up for doing autographs or pictures. However, if you ask nicely, they might do so, but please don't push the matter if they decline and leave.
Anything else you wish to know?