There's not really much to learn with tanking while leveling, most of my early hiccups were unlearning intricacies and expectations from other MMOs. If you are new, a lot of it is just going to be learning the layout and pacing of the dungeons you're going through. After that, it's about being aggressive and sure of yourself.
Make steady pulls, mark or at make a 1-2 mark macro if you're unsure of your threat, lob one target, open up on another, lay down periodic flashes, tab target enmity multiplied skills, cycle cooldowns and don't blow them in succession, stun or move out of dodgable attacks but keep things as stable as you can for the melee. That's the vague, generalized gist of it. Also, healing in the leveling game is extremely light weight and simple, so don't worry about overburdening the healer in this game, especially earlier on. (and lets be real, healers are mostly bums who stand around 90% of the time rather than aiding DPS anyway, they need stuff to do)
And of course, the obvious: keep yo' gear up to date. Especially the weapon. Grand Company will throw them at you pretty often and the weapon is the most important part while leveling.
The biggest help I had in my second go 'round on leveling a tank is that Warrior was a lot easier for me to level than Paladin. It's actually significantly more complicated but it has better tools and better AOE threat that make leveling more fun. It's probably my favorite class in the game, it's certainly one of the better put together ones right now.
