Honestly there's been a lot of good advice here. I'd definitely echo taking friends with you to start out. I know I dragged Ameline and Trisselle with me to LOTS of dungeons as I was learning to tank. 
Another suggestion that I found works well (and shows how nice the community is honestly) is that I often (and even do now) let people know when it's my first time tanking a dungeon. Usually it's something as simple as:
"Hey, this is my first time tanking here but not my first time through the dungeon."
That often let people know what to expect going in and a few times I even got some nice pointers out of it from people leveling alt classes and such.
Another suggestion that I found works well (and shows how nice the community is honestly) is that I often (and even do now) let people know when it's my first time tanking a dungeon. Usually it's something as simple as:
"Hey, this is my first time tanking here but not my first time through the dungeon."
That often let people know what to expect going in and a few times I even got some nice pointers out of it from people leveling alt classes and such.
Martiallais Heuloix - Duty. Honor. Faith.
Armand Tremaux - Justice, like lightning.
"We're all snowflakes in a great blizzard." - Virara 2017
Armand Tremaux - Justice, like lightning.
"We're all snowflakes in a great blizzard." - Virara 2017
