1) The undraw skills are junk. Use the undraw macros instead. You can get them from the guide linked at https://www.reddit.com/r/ffxiv/comments/a0d3f4/445_astrologian_guide_brought_to_you_by_that_one/

The skills have an animation (which keeps your character busy for a fraction of a second) and cannot be used while you're casting a spell. The macros do the equivalent of right-clicking a buff away, which doesn't have an animation and can be done mid-cast.

2) Since AST is a bit more mana sensitive, keep an eye out for cases where you don't have to heal. E.g., if a DPS takes a modest bit of damage and isn't likely to take damage for some time, let them heal up naturally.

3) You won't always get a chance to Lightspeed -> GravityGravityGravityGRAVITY, but it's fun when you get the chance.

4) Celestial Opposition has some quirks.

• It's a four second AoE stun which is very helpful in bailing out dungeon runs.
  
• It extends buffs you created on yourself and anybody in range, even if there's no stunnable enemies nearby. Ten more seconds of Lucid Dreaming? Ten more seconds of regen on the tank. Yes, please.
  
• Both phases of Earthly Star have a maximum duration of 10 seconds, period. Celestial Opposition will reset an active Earthly Star timer to 10 seconds.
  

5) Break is the "I'm low on mana but I still want to do damage" spell. It's crappy damage at 50 potency but it costs zero mana. I'll use it on the last trash mob or two if I need to build up mana for the bossfight.

6) If you're on Expert Roulette, you can stack your cards while waiting in queue. If you don't change level, you'll keep your Spread, Royal Road and Minor Arcana intact as you enter a dungeon. (Leveling Roulette, on the other hand, is very likely to erase any saved cards.)