In previous wow gold betas there was a noted correlation between the people.
Have a fast computer. I know, I know, this one doesn't really help you unless you've got $1500 lying around, but I'd be remiss if I didn't mention it. Cataclysm appears to feature a graphics upgrade, albeit a minor one, over Wrath of the Lich King and the folks at Blizzard are going to want to have people testing their content who can experience it fully as it was meant to be experienced. There are no hard and fast rules for exactly what constitutes a fast computer, but suffice to say if you can run WOTLK comfortably on your system then this shouldn't be an issue. Play a lot of Wow. In previous wow gold betas there was a noted correlation between the people who got into the beta and the guilds that they were in. Players with a high level of raiding progression were noticeably more likely to receive invites to the closed beta.