Posted this originally in another thread, but with all the hate on the new Astro thought I'd share it here as well. The tips are mostly pertaining to 4v4 Feast, but many are universal and can be used in any PvP.
I've probably played at least 25% of my matches up to Gold as Astro, and the rest on a mix of everything else. I've tried all of the healers and, unless nothing changes with Broil, then Astro is in a very solid place right now and can definitely be competitive. Below are some of the biggest changes from old PvP to the new PvP that need to be learned.
Lightspeed is no longer something to hold onto. If it's up and the enemy team is in DPS mode, use it. Its primary purpose is MP reduction, so take advantage of it for Bene 2 spam as needed.
Synastry is on such a short CD, make sure you are moving it between targets as often as you need to. If you heal a synastry'd target, they will receive a second heal shortly after your main one for 25% of the original.
Cards are much much better now. Draw cooldown starts immediately upon you pressing Draw, instead of when you use the card. Don't spam your card, instead sit on your drawn card if you don't have an immediate need for it and use it when you most need it.
Always be casting Bene 1, even if you only heal for 1 hp. This keeps LS spam going. You can LS every minute with the way it works now. It's crazy good.
Take Bolt and Muse as your actives. For passives, take decreased recast, increased healing potency (or resistance duration against a good tank), and increased MP regen.
Kite, kite, kite. Astro is incredibly mobile, especially with the Bene 1 into insta cast. Hug the trees, walls, whatever you can. SAM's will hate you.