Former WoW Tank/Healer. The big changes are you'll always want to use at least 1 CD per pull, stacking only certain ones so not to have all them missing when you need them. Being able to dodge avoidable dmg is big, less you take the more the healer can do other things, same goes with knowing when to use CDs to reduce dmg on Tank/Group busters. That comes with trial and error as I have learned while leveling.

Another big thing was always telling the group I was new to the dungeon for first time run. Always asked for any key mechanics I should watch out for. Example being don't stand near X position, or beware of Knockback that can send you off the edge (Looking at you Titan).

The biggest thing is finding the Tank that works for you. Each one plays a bit different and isn't a 100% it works for you right off the bat. Warrior didn't feel right for me til around the 30 mark, DRK still doesn't feel right and thats just about to hit 60, PLD feels solid like a traditional tank with the shield, and GNB I haven't used yet but went through the Job Tutorial obtaining the soul stone for it. Each tank has ups and downs, different gauges, and different cooldowns and what they do. So would be good to go over what they have and playing them each for a bit to see which one you like the looks and feel of.

There is also a Map in the form of the mini map on the radar in the corner of your screen. The full normal Map is blanked out, but most dungeons are just linear follow through Zone A to get to Zone B, etc... That starts around Heavensward. Though same thing with most dungeons in ARR, I didn't have much trouble navigating and when I did I just followed the others and they guided me through to where I needed to tank next. Doing those dungeons as DPS/Heals should give you all the clues you need as well to be able to tank them just fine for direction.

Have yet to meet anyone to tell me to leave or I suck as a Tank for not knowing mechanics or my way around. I have been given criticism to help improve my gameplay, and nudges from the healers that tell me they can handle more dmg output to my HP if I wanted to pull 2 or more packs. Those first pulls you do will determine how competent of a group you have is for dealing in AoE or ST. Just remember not all classes have AoE in low dungeons so its up to you to do most of the AoE even on the small pulls. Don't have to worry about Aggro generation as long as you have your tank stance on (Grit, Oath, etc...).

My biggest tip though, dive in, cause dipping your toe won't help you overcome any doubts or fears. It's how I started trying out different jobs and now have nearly all them at the 50 mark, and a good chunk sitting at the 60 mark. Never hurts to fail unless you give up right away. You have nothing to lose, only things to gain. Also getting friends or members of your FC to be your healer or guides as dps helps too, but I did all my experiences Solo.