Quests, quests and more quests. Lead with rogue. CC, AoE and assist DPS with the mage. IMO.

For details on setups, the wiki and stickies are your friends. Bottom line, though: there's nothing like experience to teach you how to multibox. Once you figure out what you want to do, it's just a matter of making sense of the mechanics of key broadcasting. After that, the rest is mostly just becoming more efficient and distilling things down to a few heavily-used macros that trim unneeded micromanagement from your setup.

[edit] Crippling poison + fireball spam = dead stuff. Good luck with it!