Originally Posted by
carraway
Although BLM is fundamentally simple to play, many of the decisions are highly contextual on an encounter-by-encounter basis.
Often, you will want to tie your cooldowns -- Parsimony, Excruciate, Dark Seal -- to Thundaga, but only if Thundaga can do significantly more damage than Thundara, which may not always be the case. The timing on Excruciate also depends on whether you're using AF body or not, and even then, there is going to be some variance due to the way Excruciate works. Personally, without AF, I use Excruciate directly before the Thunder leading up to the Thundaga that I'm going to fully buff.
Beyond the minutiae, and beyond gear considerations, what generally sets apart one BLM from another is casts per minute. Being able to go through your rotation as quickly as possible while slipping in extra casts (without overtaking the tank in enmity) is a key component to BLM gameplay. To that end, I highly recommend either binding /facetarget to a very convenient key (I use E) or including /facetarget at the beginning of every single spell macro. The /facetarget command allows you to force the game to recognize that you are stationary and able to cast.
Rather than say "cast X Y Z on this encounter," I would suggest taking an analytical look at your gameplay whenever you're on BLM. Look at your damage/MP and damage/second ratios, think about the timeframe for how long you're going to be casting for a given fight, and adjust accordingly.