well if you are playing correctly your runes should always be on cooldown, as for blood ones specifically, deep frost and unholy have talents to convert them into death runes, allowing them to be used for your big hits, so they tend to get used rather frequently.
Blood rune abilities,
Blood Strike (blood plague) 1B, should always be up
Pestilence (AoE plague spread and damage) 1B, will be used often as well,
Blood Boil (AoE damage), 1B, i'm not positive how often this gets used, but for AoE trash tanking its a useful ability, generally should get used before diseases go down
Strangulate (Silence, ranged) 1B for casters
Army of Dead and Death and Decay, 1B 1F 1U, AoD has situational use at lv 80, and D&D is used at the start of any aoe pull generally.
You're blood runes are your utility runes. you use them for building aoe threat and spreading diseases (which as an unholy AoE tank you have 3 of them). They also double as death runes for general use purposes, seeing as death strike, obliterate, scourage strike, and howling blast all use the 1U 1F rotation, this helps ease off your rune consumption of your direct damage runes, not to mention 1F is required for icy touch to spread frost fever, and 1U is used for plague strikes and a few other things. some abilities changed rune costs so i dont know all of them anymore.
Either way, 10% parry is huge, and those runes should be on cooldown from the start of the fight. I'd say 70-80% update, so it is a considerable amount of mitigation for a class that is known for its spiky mitigation