If you know nothing, but you know that you know nothing... that's something. Be shameless in your ignorance; that's why we came to Picademy, right? To learn stuff and junk about the Raspberry Pi. Don't be afraid to ask questions of all the Picademy staff; they are there to teach you, not judge you. (Don't be starstruck by these titans of geekdom, they are actually really nice.) You can also ask the people around you; trust me, they'll likely ask you something later and you can return the favour. Just don't be the kid who doesn't get it, but won't ask. That kid always gets an 'F'.
If a project you see or hear about looks too adventurous for you; it likely isn't. Decide on a project you think sounds fun, or would appeal to your class. Have a crack at it on day 2. You'll probably be surprised at what you accomplish, especially with the mighty technomuscle of the Picademy Guru Squad. Even if you don't get it finished on the day, you had some brilliant assistance getting started, you know you're on the right track and you've gained valable steps towards completing it. There were people on the 2nd Picademy who had never seen a Pi before who were involved in all sorts of crazy projects on Day 2; a Michael Jackson (Freddy Krueger?) glove which controlled a computer game through touch, LED arrays responding to typed input and correct or incorrect answers, electric teddybears, and my FM transmitter definitely broadcast a zombie alert over 2 floors of the building (Sorry to anyone randomly tuned into 103.3 at Pi Towers) in the afternoon... I swear.
Talk to everyone you can; network. We're all in this together, folks. If you're not on Twitter, you can get an account for free (I'm @HacklabUK; hit me up!): totally worthwhile, and one for your class is great for outings and residentials, for keeping in touch with parents and promoting your code club events. (Warning: Make sure you enable the privacy settings for a class account so it's private. Don't accept followers you don't know. Twitter is highly addictive. Before commencing a course of Twitter, see your school's AUP: I'm not a doctor.) You can bounce off each other, share resources, get your classes to work together (Skype is a beautiful thing!), or even compete with each other (Robot Wars, anyone?) if that's your bag. There is no 'I' in team. ( Sorry. Trite. I've always found that a dubious argument anyway; there's no 'I' in 'deadly rampant Zulu butt fungus' either... So?)
Get on board! There is literally everything you need to start up a RasPi lab in your school on this site (even links to shops where you can get hardware), but it all comes from people like you. Tinkerers, hackers, geeks, coders, nerds, programmers, engineers, teachers. We all want to make Computer Science awesome for the next generation of learners. If you notice anything about the team at Picademy, it's that they are all pulling in the same direction. They are hot for Computer Science, and they want to spread the love to the world, baby. Picademy is about not only giving you the right tools to get hooked up and pull along with them, but to hook others up with the knowledge too so we can all pull. Once you go back to your schools; evangelise! Turn others on to the simplicity of Raspberry Pi and praise it's openness in a world of closed off, consumer technology. Infect everyone with your hackeritis, and get them to infect other people. Exponentiality... gotta love that action.
Sign up to GitHub. Useful to the max. (Ask Uncle Ben, he loves to talk 'bout GitHub.) Get Code, make stuff. Take someone else's project and customise it, add to it, or just use a chunk of it. Post your own stuff so others can learn from you. It's free, and easy to hook up.
Take notes. There are loads of resources, leads, lessons, project ideas and bug fixes bandied about on the course, that you'll need to keep track of the ones you think sound like you might use them. Participate in discussions about things you already use too; I gained heaps of hacks and shortcuts to stuff I do all the time.
Ask Craig about exploding TNT (Block ID: 46,1). It's one of the most popular hacks in my Minecraft lunchtime sessions. Your kids will love it. Just make sure they aren't in a world with someone else's work in it. Also, renaming worlds is very handy for this reason.
Ask Dr Sam about 'MetaeX'. Open source Djing with live code...Skrillex who..? Wicked.
That's about all I can think of. Oh yeah: have fun! It's a pretty casual couple of days with positive people who want the best for Computer Science education. That sounds like you, right? Cool! Then you already have that in common with everyone else. Be chill, be positive, pay attention, have a go, learn a thing.