No matter which class you happen to play as a main, I think we can all agree upon that for normals and heroics, playing a tank or healer is generally alot more stressful than playing a dpser. Although dpsers sometimes require to cc nowadays, I've encountered plenty of dpsers who shamelessly know nothing about ccing. Why this is, I mean why tanking and healing in particular is so stressful, is one of the quests I've set out to figure out when playing WoW. This is one of the reasons I've tried to play all classes, at least somewhat, to get a good picture of what makes each role in a group more or less troublesome. There are a million reasons of course, one could probably write an essay in the subject (hmm). And I think I've identified yet one of the reasons - there are no good ways to practice tanking and healing outside the "real deal".
It always bothered me, with tanking in particular, that I had no good way of practicing tank rotations. I wanted to test how a good pull would work, how I handle unforseen things, how to best grab hold of several mobs vs one mob and so on. But right now I can't even practice a standard tank rotation, because the dummies we have have two big flaws - they don't hit back and they don't have aggro tables. The first one isn't a problem actually for Death Knights and Paladins, but for druids and warriors who get alot of their rage from being hit, this becomes an issue. And without being hit a warrior can't use Revenge at all (earlier DKs needed to be hit to be able to use Rune Strike). But for all tank classes, fighting dummies is quite far from the "real deal". You don't have to struggle to keep aggro from anyone, you don't have to bother about the mobs running around, you don't have to think about how to deal with multiple casters or when to use your cooldowns and the list goes on. There are a hundred things that the dummies won't do and help you with.
The same goes for healers, maybe even more. There is nothing about the dummies that will aid a newborn (or veteran but uncertain) healer in her task to understand how to use her spells. I sometimes spam myself to see which spells are "spammable", but that's really an extremely poor substitute for the "real deal".
So what are our options? In my case I go into lowbie instances, places where I know that eventhough I don't know which spells to use yet, which cooldowns to use when, how to aoe heal or single target heal most efficiently (which is the case right now for my paladin and shaman), people hopefully won't die. And the same thing with my tanks (although I think healing in heroics is alot more stressful than tanking right now). Another option is to pvp, in a BG you're generally alot more anonymous than in a group so people won't notice as much when you fail. This is an overall good tip, but it has its flaws as well. For one you can as healer expect to be the target of attention, and that is (hopefully) not the case in most heroics. It does make a difference in healing. For tanking you can't expect to actually have "aggro" from anything, but you can on the other hand practice locking down and interrupting players, and movement between situations (prioritizing).
The very reason I often play up alts is actually to learn more about how to heal or tank at max level. Like I recently mentioned I started yet another lowbie shaman, playing her as resto, to get a better feel at how to use the various healing skills on my 85 shaman. When you get them one by one like you do on low levels you get to test each skill thouroughly in an easier environment, really getting the hang of its usage. It is one of the biggest reasons that I play alts at all - to get to understand the class better, from scratch. With each major overhaul I have to play up a few alts because of this (usually not further than level 60 though).
The dpsers on the other hand can happily go smack a dummy as soon as they feel like they want to practice some rotations. Admittedly there are some classes that have trouble with the dummies not being "real" as well, for example you can't use your various "target is below 20% hp" skills, like Hammer of Wrath, Kill Shot and Execute. That the dummy is stationary make the results rather off from a regular combat situation too, where mobs usually run around and you have to use other skills than just dps (cc, healing). But as a dpser there is alot you can practice on the dummies, and ironically it feels like dpsers need the practice the least.
Not only that, how much practice does a healer or tank get while questing? Close to none. I remember the old Benediction/Anathema quest actually required some healing skills, but that is about the closest I've come to a challenging healing quest. For tanking I can't think of any, and in any case they're not many enough. So we get to practice dpsing alot, all of us. But what we really need is to be able to practice tanking and healing in a non-stressful environment. In an environment where we don't have to worry about doing a good job and expect to get profanities flushed over us as soon as we fail.
Wouldn't it be awesome if healers and tanks could get some sort of "battle simulation" where you had to practice dealing with various battle situations. As a healer it could be trying to keep a bunch of npcs alive. As a tank it could be to try to tank a bunch of npcs behaving like madmen (quite like dpsers in a regular heroic). These could come in different stages, or levels so that you start out with the basics and it becomes more and more difficult. There are arenas, at least in Orgrimmar, that would be perfectly suited for this. It could be a sort of dungeon, in that you're phased out from everyone else unless grouped.
Whaddya think, would this be a good way to ease up some of your healing/tanking anxieties?