When you are in charge of passing out healing assignments, you will find that everyone does it slightly differently. Some people use addons, and I'm sure these can be very handy. I have a dual monitor setup, and figure out who the tanks are going to be for each boss, who all my healers are, and make a spreadsheet assigning targets or healing duties.
For my single target healers, I sometimes have full conversations with them, via whisper. I do it privately, so that if they are having trouble keeping up a target, they can let me know instead of the whole raid - or if they find they are needing to help someone else keep up a target more than they ought to.
I Know My Class and Assume You Know Yours
I play a priest, and I know my class very well, so I can hand out a few tips. I play a Pally, and I know enough about pally healing to know what questions to ask. With Shammies and Druids, I have a general idea of their role in the raid, but the specifics, not so much. That having been said, I depend on each of the healers to know their class better than I do. Shocking, right? They're smart folks, they don't need me telling them crap they already know.
I actually do not want to make everyone's decisions for them. I don't want to control everything - I just want everything to work properly. The vast majority of the time, I don't need to tell my healers HOW to heal - they do it their own way, let me know if there are problems, and as long as the boss goes down and the raiders stay up, I'm happy enough.
I'll organize the roles so that everyone is coordinated, but all the other healers are just as good at their job as I am - so who am I to tell them how to do their job? Is that what being a leader really means? If that's the case, I don't want to lead - I want to coordinate.
Main Tank and Beacon of Light
In 25 man raids, there should usually be two healers on the Main Tank. Part of the criticism I received revolved around the fact that I did not assign this. I don't think 2 separate healers are necessary when half of your healers are Pallies since Beacon of Light allows two healing targets. Inevitably, at least one of those three Pallies will assign the MT as their BoL in addition to the assigned healer. That right there equals two healers, at least.
I guess if I'm not micromanaging the Pallies, and telling them where to put their BoL, there is the chance that there won't be a BoL on the MT. In retrospect, I think all I really need to do is ask that amongst the three pally healers in the raid, one or two of the non-MT healers put their BoL on the MT. There ya go, problem solved, with minimal micromanaging.
Instead, I decided to assign BoLs via whisper, and then realized that I was right in the first place, and didn't need to - every assignment I gave was what the Pallies were already doing. This is why I rarely feelthe need to step in and tell healers how to do their jobs - they're good healers. There is organization, and there is execution. Identifying where the source of the problem lies is the tricky part.
The point is, as the healing lead, I approach it with an eye for learning from my healers - not for forcing my lessons and orders upon them. I don't take kindly to people trying to tell me how to play my class, and so I assume that other healers won't like it either.
Yet now, I'm shrouded in indecision, stumbling around doubting my own abilities at organizing healing assignments due to problems we had on our last raid night, and the criticism I received (which is partially why I reacted so poorly). If assigning heals means that I need to be directly involved in telling every healer exactly what spells they should use when, and telling them how to play their class, then I am not the person for the job. Not only do I not have the knowledge, the patience, or the wherewithal, but I don't have the stomach for it - I am not good at just ordering people around, I am good at leading a group, together, with every voice guiding me.