Ask the other healer how he does it, and take what seemed like an advice/improvement to your style and get rid of ones that doesn't make sense to you. Ask the team if they feel like you're doing anything wrong. That's what I usually do, I don't know if it helps with everybody but I definitely realize this awkward moment exists for all healers. Even if the tank said you're not healing enough, you probably know it in your heart that you did or did not, so those "not healing enough" things are actually stuff you don't have to be told about, so yourself is also one more person you need to ask. Other than that, keep practicing and think of the rewards after beating that extra hard boss!