Yeah, drain is sometimes useful while soloing but you never want to bring it into a group situation. The heal is too small to matter when you have a healer, and your actual damage spells do so much more to the target. If you want to keep it for soloing thats fine, but i would swap it to diversion when in groups. Erase and Surecast are also fairly situational. Many dungeons dont feature erasable DoTs or dangerous push/pull mechanics. Lucid Dreaming makes a great emergency button(as a BLM you mostly use it for hate dumping, the refresh doesnt function under astral fire and doesnt matter much under umbral ice), and Mana Shift can help healers a lot(also useful to extend certain bard songs). Or Apoc as AppleJinx said.

As for the BLM rotation, Rongway covered it. Until you get Fire 4(level 60) you want to cast all the Fire 1s you can while under AF3(and get in the habit of using and maintaining Enochian if you dont already). You want to keep your Thunder DoT ticking. You want to use your procs. And when you run low on mana you need to refill. So you cast all your fire spells, then use Bliz 3 to switch stances, one filler spell will get you to full mana - this is a good place to refresh thunder, then Fire 3 to switch back to offense and keep going.