If you stick with BLM for progression and want to try to maximize it, I'd suggest starting with the basics and working out from there:

1. Do you have a solid grasp of the standard "rotation," including your best opener?

2. Are you managing to spend the absolute minimum necessary time in UI (and using the correct UI filler rotation for your stat distribution as well as paying attention to the timing of your MP ticks)?

3. Do you know to avoid common pitfalls such as using Flare/Transpose on single targets?

4. Are you managing procs correctly and otherwise always casting?

5. Are you able to use Aetherial Manipulation to good advantage when you should?

6. Do you know how to equip your BLM for mininum necessary Accuracy and to increase Spell Speed for single-target attacks (i.e. most end-game encounters).

Naturally that's not an exhaustive, super-detailed list, but if you can manage all of the above while handling mechanics, you should be fine with BLM. Knowing the fight well REALLY helps you maximize DPS so that you can plan your positioning out ahead of time and be thinking a step ahead of the mechanics when it comes time for you to move.