The best thing you can do is communicate with them. When I run my mentor roulettes as PLD (I main healer), I communicate with the healer about what I'm going to do. Am I about to do a large pull? I'll drop a waymark and let everyone know to stay here and that I'll be doing a large pull. Am I going to use hallowed at some point? I'll communicate that as well. I don't have fancy notification macros about "I'm invincible", blah blah. I just let them know ahead of time.

If I see a point in which they could do something differently or improve, after a pull, I'll take the time to explain it to them. (IE: are they using medica II when there's literally zero AoE damage happening? Explain that it may be a waste of their mana and their time could be better spent tossing out some dots in cleric stance). Try to be as constructive as possible and never sound condescending. It can be difficult, as we communicate through text, but try to toss in some smiley faces here and there, and that should lighten it up. Another point to drive home, as a WHM, it's important that they don't fall behind on healing, and to use Shroud of Saints for MP management.

And the biggest thing you can do for a new healer, is to not expect them to know what they're doing. Don't expect them to know that a tank buster is gonna hit you hard, make sure you have CDs readily available. Don't expect them to keep you topped off, and don't expect them to stance dance proficiently. The best way to ease them into learning to stance dance, is to encourage DoTs. It's the easiest thing for them to do at this stage.

Regarding regen pre-pull, I simply click it off. It's not an issue for me.