I had starting writing for this article too, and glad to see that most of my list made it to here... These are my notes that I had started

10. Unit Frames / Threatplates [covered]
9. Don't throw away sidegrades
Tanks do a lot of stat swappin to keep defense cap, hit cap, expertise soft cap, plus stam/dodge/parry at optimal levels. Keeping alternate pieces allow for shuffling around when needed
8. Train all available weapons
It royally sucks when you get an awesome tank 1-h mace, then realize your skill is 1. Take the time to get a cheapo green, sit in reguar VH by yourself, and grind up all available skills to the cap if they aren't high enough already. Do this _before_ your scheduled raid.. :)
7. Watch your healer's mana
Very much a beginner's lesson, but pally tanks especially have a habit of trying to keep divine plea up by chain pulling.
6. Know your resource
Mana/rage/runes.... know when you're too low to do the pull at hand, and take a breath or two to ensure the start of the pull goes well.
5. The Art of the pull
Different tanks pull different ways - dk's and pallys pull mobs to them, warriors charge into them, and druids... well they're screwed.. :) Usually they run into them or are forced to LoS them. Practice in 5-mans before you hit the raids...
4. Know the boss fights
The tank, more than any other role, MUST know the fight because 99% of the time, you're responsible for boss/add positioning - and that can make or break a fight
3. Know and USE your cooldowns
This includes your class cooldowns, as well as your healthstone and trinkets. If you wiped, and didn't use all/most of em - somethings is wrong. Plus consider using them at the start of a tough pull to give some breathing room for getting into position
2. quit looking at your butt [covered]
Be aware of the whole room
1. Be confident, but know your limits
A hesitant tank is a dead tank. I don't think you should pull entire instances at once - but a tentative tank is a highly dangerous thing to the raid/group. Know what you can handle, and then get them to punch you in the face