As someone who has played this game on and off I've never really got "good" at any of the classes. Sure I can do the basic content but it wasn't until recently that I've really started to put some real effort into my tanking and all I can say is...
Sorry to every single healer who has healed me in dungeons up to this point. About a week ago I really looked into trying to get better as tank as such, I've made a point of really making sure I'm using my defensives on every pack spacing them out, stacking stronger ones with weaker ones and even I've noticed the difference so I can only apologize to every healer who's somehow kept me alive before this point.
And a note to any tank out there who wants to improve, play a healer. You'll encounter good tanks and tanks like me who look at defensives and run away screaming in the opposite direction. You'll realise how much healers appreciate a tank who doesn't lose 50% of their health pool every 2-3 seconds on every pack of mobs in a dungeon.