The best way to learn how to tank anything is to just get out there and tank it. Seeing a video or two, or reading a guide for specific fights can help quite a lot, especially for higher end content (I don't really think videos/guides are too important for a lot of the dungeon-level stuff), but that doesn't translate as well as simple experience will.

If it's stuff you're new to, you'll probably make some mistakes, and you'll probably end up wiping a couple of times, but that's just par for the course. So long as you learn from your mistakes and show improvement, no sensible person has much justification to get mad at you, and if they do, screw'em anyway, your queues are instant.