Lots of good tips already. Here's what I try and pay attention to when I chain pull.
1. Cooldowns. Chainpulls = aoe, which means I need to leverage shockwave, thunderclap, cleave and revenge plus a whole lot of tab targeting. Know what's up and ready and make sure when you start with a new group you've got SW and TC ready.
2. Healer. Know your healer and their ability to keep up with the increased damage you and potentially the party will be taking.
3. DPS. Less important than the healer, but sometimes the ability to successfully chainpull is limited by the DPS ability to kill lots of mobs in a timely fashion.
4. Pull before the last mob dies on your current group. If you've got aggro good and locked, there's no reason not to pull the next group and drag what you're currently fighting to the new pull.
5. Use all your tricks. When trying to collect multiple groups remember you have lots of ways to get aggro. Charge, Intercept, Heroic Throw, Taunt, proximity are all valid ways to get the attention of a new group. If your dps has a clue, they'll give you a sec to herd a bunch together (or help with tricks/misdirect) and lock aggro.
6. Have fun.
"What we need is a special blend of Psychology and extreme violence"