Not sure if specs matter, but mine are mostly blood (down to vampiric blood), frost to annihlation and rest in unholy.
It depends on number of mobs and difficulty of mobs. You can scale down or go farther down as necessary.

Too easy mob (-2 levels), just icy touch(x5) for melee or death grip (with an alt, so mob is in range of everyone) if ranged and auto attack.

Normal (same level), icy touch(x5), blood strike (just for DPS and use runes so you get runic power). Then alternate so next mob is plague strike and maybe blood strike. Then third mob is like icy and plague only. You can make up any rotation, I just like to use different ones so I use mostly all my runes.

Medium hard (+3 levels or -2 levels elites). Pick biggest mob first, since I need it to have a lot of HP so it doesnt die fast. Icy touch, plague strike, pestilance, blood boil (or blood strike--up to you). I just try to burn my blood runes, cause they are helping (DOTs ticking on mobs while I am busy killing one) and make the blade barrier (no blood runes makes parry go up) helps. Then when really hurt or on second mob (diseases last longer due to unholy talent--like 2-3 tier), death strike to get health back. Usually mob is dead. Can just wing it after that.

Hard (+6 levels or +2 level elites). Again, pick biggest (most health, doesnt die so fast). If you don't like a mob (mean caster, ranged, etc), just pick it first since it will probably still have enough health since it is higher level and it will probably die pretty fast after you get your diseases spread. Icy touch, plague strike, pestilance, blood boil (or blood strike if single mob only, otherwise boil--want healing from damage--blood aura). If you can wait for 2nd mob, just auto attack, if not, death coil 1 to 2 times, and then death strike 2nd mob. I like to run with 100% runic power normally, it makes death strikes HUGE (glyph) and gives me a way to do anthing I need if poop hits the fan.

Basically I don't watch runes except for blood since I deliberatly burn them at the start. The others I get a death rune (talent) for anyway with my death strikes, so I don't worry about them. I have never really had a time that I didn't have enough frost or unholy runes. It probably depends on spec though.

Hope that helps.