This is the first game I ever tanked in.
I did a lot of flashpoint leveling on my first tank character. Never had a single problem with any group. (If I didn't know a fight, I let 'em know.) I think what made me better out of the gate is that I had some healing experience on the other faction, so I was comfortable with watching the overall group situation and used to keeping my eye on people's HP.
People in pre-50 were pretty laid back, to be honest. Think about it: flashpoints aren't the fastest way to level, so the hardcore "plough-through content" types probably probably aren't there, anyway.
This is also my first MMO that I tanked in. Normally I play DPS but I decided to do something different. I had zero issues in the level 50 non heroic FPs. Simply told people to give me advice on how tank it and they did.
The non heroics FPs are also...very easy. You have room to screw up and learn before you hit the tough stuff.