The best way would be to go to EJ and read everything.
I assume You know only tanking spec now is Blood and DS heal and gives Blood Shield that absorbs dmg for amount healed+mastery
There are still huge debate on what stats DK should prefer but if You are going only 5 man heroics I guess both avoidance and mastery should be used.
So first of all - forget about stamina gems. Remove, delete, sell or whatever You want, just don't use them.
Meta - Austere Shadowspirit Diamond (stamina + armor)
Red/Yellow - Fine Ember Topaz (parry + mastery)
Blue - Puissant Dream Emerald (mastery + stamina)
Expertise keep at 17 for holding agro without any problems
Hit mostly ignored but its up to player, how comfortable he feels.
Dodge / Parry now have same Diminishing returns so keep them as close as possible
Mostly You will use only 5 spells - Rune strike (main TPS); Heart Strike (Blade Barrier); Death Strike (heal+bs); Icy Touch (debuff) Plague Strike (debuff). Of-course DnD, DG etc But its more situational / aoe.
That should cover mostly You should know for starting
If at first you don't succeed, you are running about average