Given that many people are trying new things in Cat, I figured I'd write a guide or two on various things. This one is on click-casting, keybinds, and how to figure out what to bind to what.
First off, what is click-casting? It's the ability, primarily used by healing classes, to mouseover a target either in raid frames or party frames, and heal them with a click. It's faster than selecting the target, then hitting a heal.
Second, how do I do this? Well, you have several options. Me, I use the addon Vuhdo, which is a raid frames and click casting addon. Other people use Grid (a raid frames addon) and Clique (a clickcasting addon) together, or simply use mouseover macros and the default frames.
Here's the vuhdo wiki.
Here's a couple blog posts about how to setup Grid and Clique.
Here's some info on mouseover macros.
Third, what do I bind to what?
Okay, this you want to think about carefully and have an overall strategy for. I'll walk you through my disc priest setup for Wraith to give you an idea.
First I figured out what buttons I can use easily. Since I play on a laptop and use a trackpad, I really only have left and right mouse buttons. But vuhdo allows me to use ctrl, shift, and alt, as well as combinations thereof, to modify my clicks. The combinations aren't really workable for me, so I'm left with 8 click-casting options.
Left click and right click: these two are the easiest and fastest for me to hit. So, I bound my two most-used spells to them, Power Word: Shield, and Flash Heal. I changed Flash Heal to Heal when Cat hit, but the sentiment of "most used" is still there.
Ctrl+left click and Ctrl+right click: big heals. I bound my two biggest single-target heal spells, Penance and Greater Heal, to these two buttons. Having my two big heals use the same modifier button helped me remember the bindings when I was learning them.
Alt+left click and Alt+right click: select target and levitate. Alt+left click is actually the easiest for me to hit, so it made sense to me to bind something I use a lot there, plus I needed some way to select people from raid frames. And as for levitate, well, I like having it keybound, and when I had a heal bound there, I kept forgetting about it. So it made more sense to just bind non-healing functions to alt.
Shift+left click and Shift+right click: I never used these in Wraith. I believe they were bound to Renew and possibly Prayer of Mending, but I'm not sure.
Since I'm limited in my click options, I tend to be picky about what I bind and don't bind. If I generally only use a spell on one target (renew, prayer of mending, earth shield), or the spell has a cooldown (pain suppression), or does not need a target (circle of healing, holy nova, power word: barrier), I don't bind them to mouseclicks. All those spells are bound to my number keys, and that's how they get cast.
So when considering what to clickcast, and where to bind it, consider:
like functions (aka big heals all using the same modifier button)
ease of clicking (aka bind most used to left and right click)
how spell is used
It's important not to overload your brain. Start small, maybe just with left and right click bound, and gradually increase. If you're moving to click-casting on more than one toon, try to keep the philosophy consistent. For example, my leveling resto shaman has her fast heal and her to go heal bound to right and left click. For my druid, it's regrowth and rejuvenation. For my pally, it was holy light and flash of light (but I haven't looked into pally healing since 4.0).
Hopefully this will help make the wonderful world of click casting less scary. It's my preferred way to heal and I think once you convert, you'll never go back.