I keep everything on my hotbar except like undraw and benefic 1.

It just takes practice and muscle memory. Like just go to a training dummy and just press all your aoe heals one by one (weave ogcds in a gcd) and then all your single target heals and then malefic until it comes off cd and keep doing that. And then just play a lot, especially things that are chaotic and people mess up like msq trials, lv 90 normal raids, pf clear parties, etc.

Don't worry too much about avoiding overheal or using the optimal skill until you are at that level. Just keep people alive first, then focus on uptime, then focus on using your buffs correctly and only last is optimizing healing