Druids and Paladins both have addons that tell you exactly what to use when.
I find it strange that Death Knights do not (or at least I didn't see one listed at Curse).
Situation: My mom plays WoW. She's 55 and she doesn't have a fast hand-to-eye coordination, and she has trouble seeing the itty-bitty little rune icons at the top of the screen and she seems to be a bit slow in understanding why I told her to use the buttons in the order I told her to.
That and I think she's not watching for misses on Icy Touch and Plague Strike, or she uses them too often (and doesn't have any runes for Obliterate (which I never put on her hotkey bar, to avoid confusing her) or Death Strike.
Basically, I told her to use "3, 4, 5, 5, ="
3: Icy Touch
4: Plague Strike
5: Heart Strike
=: Death Strike
6: Death Coil
And she does that for the most part. I know she SHOULD be using Death Coil, but she usually forgets. Blah.
Anyways, Paladins and Druids have this thing that pops up on the screen and tells you what you should use next... anything like that exist for DKs?