I had similar concerns (made worse by the fact that I decided to go WAR). I made it to 38 BRD before switching, so the last few dungeons especially were a little nerve-wracking, going through 1st time as a tank. For me, the community has been very good. There's always the occasional ragequit after a wipe, but the vast majority of people have been helpful and patient. Do your research, practice emnity stuff (rotating enemies, etc), ask for help and hopefully your experience will be as pleasant as mine has been.
Also, I thought this was a great guide (especially the UI section in part 2): http://eorzeareborn.com/tanking-basics-communicatio/