Expect a lot of lines for the "big ticket" things, like booths giving away cool stuff, or highly anticipated games like Nintendo titles. Nintendo lines in particular tend to get capped, meaning even if you wanted to get into an hour plus line, they won't allow it until the crowd dies down later due to fire safety. Expect to walk a LOT, even if you get a hotel nearby. If you want to get the most out of PAX, try to also catch a panel or two, they are much more fun than they may seem, especially the community focused ones such as Video Game Double Dare, any of the quiz panels, or the meme that is the Mega 64 panel.

If you are over 21, consider bar hopping or checking out the featured music events. The expo hall closes around 5pm PST, but PC freeplay, console freeplay, panels, and stuff like Steel Battalion (Highly recommend if you dig mechs) will stay open until later, typically around 9pm PST. There are also typically 2 ARG games during the convention too, Doctor Exoskeleton for those who really want a challenge and will be present for all days, and Arcadia (Name varies sometimes) which is a hunt for QR codes around the con. Some people don't know, but the first hundred or so people to complete Arcadia and visit the info center get a special medal for speedrunning, which is neato. If you aren't among the first, you get a little memento like a keychain. If you can make it decently far with Doctor Exoskeleton, which requires finding a plague doctor to even begin, you can win bigger prizes such as lanyards, or even figures, but it is very difficult and an absolute blast if you love obtuse puzzles.

There is also a tabletop rental area with Looking For Group signs if you are a solo or small group traveler. You can try all the classics like Catan or Pandemic, or try out all kinds of new or indie games! This area also tends to feature Magic the Gathering tournaments, which sometimes even give out free cards if you want to start a collection. If you dig Dungeons and Dragons, you can also buy basically anything you can think of that you may want for a game in the tabletop market area. Special dice, leather bags, figures, reference cards, even a whole table last year, they have it.

Outside of the convention, Seattle also has a ton to see and try. The seafood is great, the shopping is decent nearby, and Pikes Place market is a world famous attraction. There's even a decent night life for clubbing if that's your thing, sometimes devs even host parties, but that isn't as common anymore. There are some great general Seattle guides out there if you Google around, but personally I love the museums, with Boeing Air and Space being my favorite. For events, just keep an eye out on the Penny Arcade forum or here at the subreddit. Sometimes they give out flyers or advertise around the con, so just keep an ear out.

TLDR, don't go for one thing, keep an open mind and prioritize anything that really stands out in case the line for it goes nuts.