Heya fellow Tanky! ^^
Good job so far on making it this far.. you are almost done to get to lvl 50, and there will still be lots of fun awaiting you!
*I type a few words on a post, then click the EDIT: you will have unlimited character (don't ask why SE did that, please don't)
Before the fight: you mark your targets (now you can go up to 5 with the standard symbols) usually its 3.. I will mark 1 and 2, the last one is obvious.
I don't macro Skills with markers: since you will use them often, it could change the target's numbers, mkaing it a bit difficult.. but that's me.
DPS and Healers as well.. need to let you build aggro.. a bit before engaging and blasting everything to smithereens.. That's their part of the battle.
As others mentionned, your job is not DPS, but making sure all enmity, enemies are on you, at all time, until depleted of their HP. When you know the mechanics of some mobs, you will be able to turn around so they face you and not the rest of the party. When they do their AoE skills, you move out, and then back into the last position (will help melee DPS and their combos)
For Provoke, i prefer the approach of clicking on the mob that escaped your grasp, or was never into play, but suddenly appears. so for me it's <t> and not <tt>
if you marked 1-2 on 3 mobs, and then 2 other joined.. Make sure you will flash and aggro them, your hate on 1-2-3 should be already decent. By the time 1 and 2 are down, you can mark the 3rd one with the 3, and then once he's about to die, you can reuse 1 and 2 to mark the remaining ones, or as I said, now you can use 4 and 5.
DPS can easily catch upon their own meter and checking the lowest one with HP to kill. Then since 2 other joined, they will check which one you are targeting, and should hit them, if you didnt mark any. (lots of Tanks don't mark, so you have to use other methods)
I would say keep on marking, in case you encounter rude party members. If you wipe, and it was marked down, you stated the order in which they should have focused. So no blame on your part.
If your gear is lower, state it when beginning, so they will wait until a few shots on your own before as well. (it's pretty much always the same patterns..)
If you are with BLM, BRD (and you will) they should be able to use their AoE skills.. like the super Flare!
Making sure you build enough aggro, being properly geared for your lvl (including the next best weapon that you unlock) and THEM letting you get aggro a bit first: no wipes, no issues.
It's a TEAM effort: you carry some pressure on your shoulders, but not all. Very big difference here.
Don't let a rude comment get to you, unless it's very bad. State that you are new to Tanking, new to the particular dungeon, open to any tips, and you will see more people willing to give you advice, than the rest..
Good luck, you are doing this game a great service ^^