Stagedooring 101:
MOST IMPORTANT- If you did not see the show THAT DAY, if your ticket does not have that day printed on it, if you didn't even see the show--PRIORITY goes to the people coming out of the theater who actually saw the show. I've seen a bunch of people who get their photos and autographs, and then step back to let the people behind them have a chance. I had an awful experience at the DEH stage door where I saw the show and then wanted to stagedoor. I ended up in this corner, where there was also a barricade for people who had not seen the show, but still wanted to greet the actors. An awful woman put her arm over the barrier so I couldn't get to the front. She kept moving her arm, and I think she was even bragging about how she hadn't seen the show but she was still going to meet the actors. I said "excuse me" so I could put my arm there, since I'm short, and she was incredibly rude in her response. Eventually I ended up just putting my arm on top of hers or next to it and slightly pushed it away so I''d have enough space to get my playbill in a place where the actors could see it.
Otherwise, I've had very positive experience. If you didn't the show, wait. People will move, they will pass playbills forward, they will help you if you ask for pictures. I know that happened when I stagedoored Jessica Vosk's first show at Wicked. We all helped each other.
Main thing, be polite, remember everyone will help you if you ask, and DON'T PUSH. Also, wait by the end of the barricade if you haven't seen the show. Some actors do start at the end, so you might even get to them first, even if you didn't see the show that night!