How do I optimally spend MP?

Ideally, you should use 5 Edge of Shadow in each 2-minute raid buff window (except for the opener, where the first edge is used early to get the Darkside buff started). To do this, you use 3 MP spenders in odd minutes, with the last one being The Blackest Night (TBN), and hold the Dark Arts from this TBN breaking until the buff window.

Can I use all my MP on The Blackest Night (TBN)?

Up to 3 (4 with careful timing, by using TBN during a buff window) MP spenders per 2 minutes can be TBN without losing any damage — all three spenders in the odd-numbered minutes, plus one in the even-numbered minute. Note that the damage loss from using TBN more than this is smaller than the damage loss from dying! It is always better to lose damage in buffs in order to stay alive, and sometimes even to reduce the amount of healing needed.

Why don't we use Living Shadow prepull/Should I use Living Shadow during phase transitions?

Using Living Shadow prepull can result in some of its damage coming out before raid buffs. For some phase transitions, you may nevertheless find it useful to use Living Shadow early (up to 6.8s before the enemy becomes targetable), either because buffs are being used immediately when the enemy returns, or because a tight phase timing means that you would lose a usage of Living Shadow by delaying it.

Why don't we use Delirium earlier/prepull?

Using Delirium prepull leads to MP being generated too early, forcing an Edge of Shadow outside of buffs (at the 2 minute and subsequent buff windows). Some fight circumstances may lead to this still being worthwhile, but in general, the later placement of Delirium is better.

Why are the oGCDs in the opener ordered the way that they are?

The opener is laid out to avoid overcapping on MP both in the opener and in future burst windows, and secondarily to maximize the damage you do if the fight ends in the middle of a burst.

What GCD speed(s) should I use?

Use whichever speed feels most comfortable. 2.50 has perfect alignment between GCDs and oGCDs, but may not always be achievable depending on gear options. 2.45 has good alignment with perfect play, but 2.46 gives slightly more leniency than 2.45 at the expense of slightly worse alignment in the optimal case.

What food should I use?

(Patch 7.0/7.01): Either Vegetable Soup (for DH-focused sets) or Fruit and Aloe Jelly (for crit-focused sets). You can compare the two in a gear calculator to see which is better for your current gearset.

How much mitigation will I gain/damage will I lose by focusing on Tenacity?

Every 24-25 points of Tenacity give 0.1% additional damage, and every 13-14 points give 0.1% additional mitigation. For comparison, every 19-20 points of Determination give 0.1% additional damage (and no mitigation). For 7.00 best gear, a full focus on Tenacity gains approximately 6.2% mitigation and loses approximately 0.8% damage compared to the best damage melds.