@trigger, if you're looking at the website. I wouldn't bother, its never up to date. It's been booked out before and still shows as spots available.
Hope I'm wrong for your sake, other than that just get there at 7:40ish to guarantee walk on on the day.
And regarding tips, llukiie, take a torch for starters. Peacocks is generally where games are won and lost. Basement is often bottlenecks, the corridors behind the shops are great for flanking. Always watch out for the balcony if you are on the main concourse. Most of all, have fun!