Hit what the tank is hitting, it will increase your chances of not pulling aggro. Also, the second thing I was taught when I started doing instances (after "wait for three sunders" ) was "if you pull aggro, run TO the tank so he can get it back". Of course if you have multiple mobs on you, that's your bad for trying to AoE the pack instead of burning them down one at a time.
oh and i always love the tanks to when you pull aggro,and you walk around with 10 mobs on you and the tank doesnt even relize it and just keeps hitting away at the mobs hes tanking
OT: Raiding tanks simply have very little incentive to do heroics. To be honest, I haven't had too many issues the few times I've pugged something, it's just that it's not a good use of my time. There's only two of us (tanks) splitting all the raid drops and if I don't have my valor cap for the week, then my dps and healing guildies definitely don't have the cap and I can do a guild run with my friends.
Suggestion #1 - something I haven't seen suggested yet (although I haven't really looked) would be to add some extra health to all the mobs in heroics and then make them 6 man runs with one extra dps slot. Keeps the same Tank/Heal/DPS dynamic but increases the available dps slots by 33(?)%
Suggestion #2 - really up the reward for tanks who use the LFD tool or change the reward mechanic from "small chance for something cool" to "doing X number of LFD uses guarantees something cool"
How does a PC gamer change a light bulb? He doesn't. He goes on the forums and QQs about it being dark.