This will be my first time using those features, I need tips on how to do them right. Spot pass is apparently on a per game basis, does it require the game to be in the cartridge slot, turned on (the active software) but paused? I have Mario Land, Ocarina, Snake Eater, Kid Ic, Paper Mario, Layton, Tetris Axis, and a few more. Is spot pass the thing were your street fighter characters will have silent cpu vs cpu matches? For street pass, I've heard the GB crew claiming that it only does ten at a time, meaning even you pass a line with 200 people waiting in it, you'll only street pass with the first ten you're near... Is that true?

SpotPass is just the feature where the 3DS will automatically download new data (patches, new videos, new weekly add-ons to games, etc.), assuming your 3DS is connected to a wi-fi network and is powered on (doesn't matter if the lid is open or closed, it will update as long as it is powered on and can access the internet). SpotPass is not particularly relevant to PAX.

StreetPass is the thing where your 3DS is constantly looking to exchange data with any other 3DS that comes within like 30-50 feet of it (again, the 3DS must be turned on, but it doesn't matter whether the lid is open or closed). By default, every 3DS has StreetPass Mii Plaza; it has 2 mini-games, a game where you trade puzzle pieces, and a very simple RPG where you only progress by using Miis other than your own and they fight for you. StreetPass Mii Plaza shows you the primary Mii of every 3DS that your 3DS has come near. StreetPass Mii Plaza is the easiest thing to check while at PAX, because it only takes a minute or two to trade puzzle pieces, and play the simple RPG.

Individual games can also have StreetPass functionality, but not all games do. You don't need the game to be in the slot, as if the game supports StreetPass, it will make a save file on the SD card in the 3DS - that way, you can have multiple StreetPass possibilities at once. Most games ask if you want to use StreetPass either the first time you boot them up, or when you get far enough in that particular game that you unlock the ability. Most of the StreetPass things in actual games are amusing little side distractions, and while cool to know that people you walked by are helping add more stuff to your game, they're not super important; it varies a lot from game to game.

It's probably not worth playing Super Mario 3D Land (or whatever individual game) every 5 minutes to keep "using up" each new StreetPass you get. You'll never keep up. However, I do encourage you to poke around in each game and make sure you have StreetPass enabled (Google to see which of your games use it), because you'll come home and find the StreetPass-enabled games have probably hit their limit of new StreetPasses.

So the important part for PAX is: leave your 3DS powered on, but shut, in your pocket or bag. Unlike the usual North American sidewalk, bus, or train, PAX will have a silly amount of 3DS' per square foot, so you will get people constantly. The Mii Plaza is probably the only thing actually worth checking while you're at PAX, because the whole structure of the games I mentioned earlier is that you make progress the more StreetPasses you get. It does fill up quickly (I think the limit is 10), so feel free to check it whenever you're waiting in line, or sitting down to rest for a minute, or whatever.

The poster above had said it all, you just make sure that your streetpass and spotpass are turned "on" in the settings of your 3DS and don't forget to do so too for each games that have this feature. You don't need the cartridge but you do have to at least have used the game at some point and enabled your streepass on them.

Again @bisonhero had said it all, he gave you all the informations you need.

Have fun at PAX, and collect ALL the Mii!

The best strategy to street passing at PAX (street paxing?) is being at PAX.

Be prepared to clear out your Mii gate every 5 minutes.

I can't wait to collect a bajillion puzzle pieces when I'm at PAX AUS in July.

Thanks guys. But is it ten per game or ten overall (like five people give me plaza stuff and five people give me Ocarina of Time 3D stuff, then they're all full?)

I found the perfect time to do it is while waiting on a line, sitting waiting for a panel to start, taking a break from all the walking. Of course you can check it more often than that. Surprisingly you also get a lot of StreetPasses at your hotel. At least I did last year. Finally make sure your 3DS is updated. I didn't know there was an update and after I got back from PAX it updated at home and I found out there were tons more puzzles. Ah well, I'll finish them this year.

Everything is independent. It is 10 for StreetPass Mii Plaza. For Mario 3D Land, it is 3; Fire Emblem is 50. It varies. One person's 3DS can register a StreetPass in multiple ways at once. You can check this in the upper right if the main menu on the 3DS; your notifications inform you of your current unchecked StreetPasses.