As someone who went Healer > DPS > Tank, here's a few extra things I'd say to help you out. The best things I'd say to start out with:

1: Learn how to position. There's a picture out there somewhere that goes a bit more into depth about it, but basically you want YOU - MOB (back) - Party. This ensures that most of the AOES are coming to you and you only. The best way to do this is to use your distance pull, AOE emnity, then run THROUGH the mob to the other side. It works well. (I don't know the DRK skill names I'm afraid).

2: Cooldowns are not JUST for bosses! Use them for pulls, I promise they will come back in time.

3: You and your healer are working together (as you know). If they are falling asleep at the heal, then you may have to use even more cooldowns, or pull smaller groups.

That's the basics. You can do it, tanking can be a lot of fun. You may mess up, it's okay! A wipe is just gaining knowledge. Good luck!