DK + 4 rets - struggling in heroics

[Zugdud]

I agree with the 4x ret remark unless you really want to play with a holy paladin, once you get used to playing this team and gear up you will find heroics are a breeze and can be cleared quite fast. I have not yet had time to try the ICC instances, but everything else is very doable in my experience. When I started out after hitting level 80 I found ToC a bit too difficult and stuck with preToC heroics which are far easier in comparison until I was geared. The most important things to master are good management of AoW on FoL procs, maintaining four sacred shields at all times, JoL, and divine storm. That alone will see you through most encounters, situationally you may find AOE damage overwhelming and in these cases you can always use 1 or more divine sacrifices in rotation

Having a good way to control your heals is pretty key, my personal preference for healing is 5 dedicated keybinds where each is a macro to drop 4 FoL on a specific toon

Good luck!

P.S. A tip for the puddle bosses like Colossus is to just kite him while tanking and dpsing during the elemental phase, that allows you to avoid a majority of the damage