Quoted from roar:
A piece of advice I would give after experiencing Allentown for the first time myself last year is to not be afraid to speak up...
Talk to people, I'll second that for sure.
For the most part, pinball people are pretty easy going. Sure, there'll be a few idiots who have no idea how to behave in social situations, but that comes with any hobby where grown men play with expensive toys! The best ice breaker is to ask to start a multi-player game with a stranger. In conversation, ask people what they've played so far: there may be a game a few rows over you've skipped/ignored that's worth a look. Or one that's super rare that the opportunity to play one may not arise again.
The market advice here is spot on, too: plenty of people looking to add games, and plenty more (like you) looking to get into the hobby with their first. If you see a game you want, and its at a price you can afford, act! Excessive tire kicking or walking away to mull over may hurt your chances of buying. Friday is the best day for selection. Saturday may see some deals at the end of the show, but they'll be hidden amongst the junk that people brought to put on the floor to get free admission and now don't want to bring home! There will be a few "retailers" in spaces near free play area with a few games set up for sale. In my experience, prices of these games will reflect the fact that they are retailers.
Good luck...hope to see you there!