From my perspective, there are 2 ways to play BLM, Thundermage and Firemage.
Thundermage:
This playstyle relies heavily on crit/det as your secondary stat priorities. This playstyle is very effective in Frontlines, not so much in Feast. Bread and butter of Thundermage is Swiftcast->Sharpcast T3, guarentees you a proc and you toss the proc on a second target. I personally like to spread T1 after that on different targets and fish for procs. The bulk of your damage here will come from Scathe and Thunder procs.
Firemage:
This is probably what you want to start with and fit it to match your own playstyle if you want an all around style for Feast and Frontlines. As mentioned by others, main source of damage here comes from heavy F4 damage. You can either prioritize crit/det as before or Spell Speed/Crit (Which is what I do).
My typical opener is:
Swiftcast -> F3 -> Sharpcast -> Enochian -> F1 -> Raging Strikes -> F4 x2/x3 -> F3(Proc for damage and reset) -> PD
