just a lil advice for those willing to lvl their Cleric with the only purpose of healing in Dungeons to get an easier time at getting a group, but aren't willing to play 'em as a main class.
Focus on your Healing spells, don't even bother lvl'ing the Damage ones... get into 3-men and kill trash mobs (wearing a shield and a mace if your Cleric lvl is lagging way behind, or an axe if it's close to the dungeon lvl). Once you get to the boss, exit, reset, rinse/repeat... Takes a bit, but saves you ALOT of money from spells you won't need in the end. Also, dungeons trash mobs class XP is MUCH better than quest ones.
It will also help you get a hook of your class
I know that way won't fit to everyone, so feel free to use another way if you don't have the patience for it. It's very rewarding in the end tho.
@ Tehmo3 :
Doesn't matter really, classes don't share anything but the Certificates, and lvl'ing a class at 10/20 for a Certif you think you'd want is a matter of minutes