I'll start with a guide to creating a new cleric in Rappelz, however, and lead on from there.
The meat of this guide will be the part intended for higher level clerics, though. So skip down to the next section if you're already doing dungeon parties. I'm going to illustrate how to play a *good* healer here - how to play one 'professionally'. If you follow this advice, you'll be in the 5-10% of truly competent clerics in the game.
Playing a mediocre cleric still requires a bit of attention, but playing a good one is somewhat complicated. So bear with me as I get really detailed for some of this guide. A lot of these things will come naturally to you after enough time, but it's important that you establish these good habits as soon as possible(rappelz rupees).
If you only scan one part of this guide, read the part below labeled "MP Conservation" and "Healing Strategy".
--- Advice on creating a new cleric ---
Playing a cleric at the very beginning is much like playing any other sort of character. Your goal here is just to get to level 25 or so. After that point, you should only be doing dungeon parties. You *can* solo at any level to some extent, of course, but other classes are much better at fighting. Don't frustrate yourself by attempting to do it with your cleric - just make an alt to solo with when you don't want to group with people and heal(rappelz gold).
Staff Mastery - (you only use a staff for the M.Atk, to boost your heals, and Staff Mastery only boosts the P.Atk mildly.. thus, it's worthless. Don't waste your JPs)
Mace Mastery - You can put 3-4 points into this to get you through levels 1-25 if you like. After that, you'll never use a mace again (if you're a good healer). If you want to solo later on, put more points into it then.
So, do quests till you're level 25 or so. Focus on raising your heals as much as possible, along with Wizardry Mind and Mental Amplify(rappelz rupee).