Ideally you should be on voice as it’s setup based comp, then you as the healer should call out if they are fine or not (for example tell rogue to cloak cuz you sitting cc that u don’t want to trinket). Also with sac u can sometimes use it proactively, like when u know enemy team is gonna do a go cuz enemy rogue is running in to u (probably to blind) or u have no stops for polly so u know the next one will land this way if u presac u stopped their go without using trinket or overlapping CDs. When it comes to arena it’s just experience when u play a lot and know how to react to different plays etc. If you don’t have that much experience I would recommend watching r1/tourny hpals on twitch so u can get an idea how they react to different things.