- Read the stickies. (-:
- Don't feel bad about going Ret to 60 or 70 before going prot; it might make it faster.
- Make sure to practice tanking at least one instance every 5-10 levels on your way to 60.
- Try to tank as many different instances in Outlands as you can on your way to 70. After level 60, you should have the core of your tankadin build fleshed out, so things don't change a whole lot (aside from itemization improving by a TON once you can equip some of the level 70 gear).
- don't be afraid to heal your way through some instances (I healed Ramparts 6x, tanked it 1x), if that's the way to collect the gear you need.
- Consider tanking instances when a level more than what you "could" do it at -- avoiding crushes from Hungarfen and friends can make your healer's life easier... esp since you likely don't have as much stamina as you'd like while leveling.
PLG+Shield spike is a great threat source when aoe tanking, if you can otherwise gear appropriately.

When you can get it, it may be one of the better shields available, too.
- remember that PLG's poison will break sheep/ice, and thus don't chew out CCers as readily.
- prepare to spend $$$ on BOEs and stamina gems at 70, as well as avoidance/defense enchants/armor-kits.
- Work on caverns of Time reputation. The legs are awesome.
- Don't skimp on cheap gems for things you will wear for a long time (e.g., starting 70 gear)
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Don't lose heart. It'll only get easier.