My opening rotation for T8:

Hard cast Shadowflare as Tank is running to boss
Auto attack, Raging Strikes, Bio II, Miasma, Bio, Miasma II, Ruin II, Fester, Contagion. Rouse, Spur, Enkindle, Ruin, Fester, Ruin II.

That last Ruin II gets in half a second before Raging Strikes wears off. Swiftcast Shadowflare, then reapply dots as they are about to fall off. I only use Miasma II when I have contagion available for more mp for Festers.

My T9 opener is the same except no auto attack and no Miasma II.

Not saying this is the best opener but it works for me and I am usually highest DPS at start of every fight unless our BLM gets some good crits or rng procs.