i found some guide on another forum, maybe it will help you to find a good build to be a master of healer.

Priests are the supportive type characters that can buff and heal your party members. Priests tend to "leech" exp on parties alot at low lvls, but they do have some high-dmg skills too to help them on quests and solo. But I wouldnt prefer solo to any priests, they should stay at parties as much as possible, especially with bladers. You can always leech exp partying with bladers at low lvl, with swordmen and bladers at mid lvl, with everybody (especially spearmen) at high lvl. Now even it says leech exp, it doesnt mean you just can afk on parties, you will need to buff and heal them constantly which make the leech sounds more difficult. Otherwise priests are the ones that may constantly hear something like: "Buff me plzz" or "Heal me fasttt". Priests are also very good at soloing bosses.

Theres 2 good builds for priests:

Buff/Heal Priest build:

From lvl 1-10 you will have 9 skill points to add.
Raise your first skill to lvl 9 - first skill raises your regenation speed of hp and mp.
From lvl 11-20 you wiill have 10 skill points to add.
Raise your fifth skill to lvl 10 - fifth skill raises the amount of hp you heal.
From lvl 21-30 you will have 10 skill points to add.
Max your fifth skill [max lvl 20] - Now you will be able to party ppl that are alot higher lvls than you and "leech" exp from them.
From 31-35 you will have 5 skill points to add.
Raise your first skill to lvl 14 - Important since you need to heal alot, you need alot of regenation to lessen the pot using.
Ok heres the best advantage for Priests, that from lvl 36 onwards they will gain 2 skill points each lvl. Thats mean From lvl 36-40 you will have 10 skill points to add.
Max your first skill , now you still have 4 skill points to add.
After this you can max your fourth skill - fourth skill raises your mp.

Nuker Priest/Battle Mage build:

Maybe the best soloer class, you can heal yourself plus do great damages.
From lvl 1-11 you will have 10 skill points to add.
Raise your second skill to 10 - second skill lessen your mp use.
Ok here comes the critical and frusrating part of this:
After the 1st rank up quest (lvl 10) and when you are lvl 11 delvl back to lvl 1, you will lose all your skill points you added to second skill.
Now lvl back to 11 to have 10 skill points again.
Raise your sixth skill to lvl 10 - sixth skill raises your magic/skill dmg/power.
From lvl 11-21 you will have 10 points to add.
Max your sixth skill [max lvl 20] - Your magic dmg will be rose by 40%.
From lvl 22-30 you will have 9 points to add.
Now raise your second skill again to 9 - important since from now on you will need to rely on your skills.
From lvl 31-35 you will have 5 points to add.
Raise your second skill to 14.
From lvl 36-40 you will have 10 points to add.
Max second skill [max lvl 20] and you will be left with 4 skill points.
Add all to first skill - regenate speed.