Keeping in mind that EF is changing on the PTR (significantly), addendum to what Heidi has mentioned:
* EF is your highest HPM spell you have, despite the cost. If there are > 4 people in range (25y!) then it's well worthwhile to cast. That it only has a 25y range, is Blizzards gift to MW.
* Corollary to above: EF gets more usage in raids than dungeons.
* Absent extenuating circumstances (below), you'll definitely want to follow up EF with direct heals; the EF hot causes the mastery heal to be applied twice; note: for vivify, this means the primary target only. Cleave targets don't count.
* During innervate you'll definitely want to spam EF, assuming first point above holds. Once you get 4pc, spamming becomes less attractive, as you want to weave in direct casts of vivify , to take advantage of the extended hot
* Mana Tea becomes very attractive, if you find you're using EF a lot. I think you want to go Ef-V-V during MT (haste permitting), but I wind up going full HAM on EF spam.
* (mostly) never use TFT charges on EF