Last Chaos Gold is the key to win. Here I will introduce you something about guides on knight and healer. I hope you will like it.
1. Knight
Level 1 - Level 7: Knights are more efficient in defense, so you might have to stick with hunting Fox during level 1 to level 2 or 3. Beyond that period is hunting wolves.
Level 8 - Level 10: Jaguars remain a good source of experience. Potions are a must and you should have armors and LC Gold up-to-date.
Level 11 - Level 14: Sasquatches, like Titans. If you use dual swords or Cheap Last Chaos Gold, which is recommended, you should not have problems here.
Level 15 - Level 17: Horn Beasts, horn beasts, and more horn beasts. Drakes are good as long as you have a party with a healer.
Level 18 - Level 20: You have a choice, you can either go train at Dratan, Dark Goddesses or Prokion Temple; or, you can stay at Randol and go hunt some Drakes. It is up to you to make that decision.
2. Healer
Level 1-Level 5: With your trusty bow in hand, go out there and put the hurt on the foxes and wolves that roam the grasslands of Randol.
Level 6-Level 10: You really do not need healing potions at this point since you have the Self Heal skill and Buy Last Chaos Gold.
Level 11-Level 14: Sasquatches, if you are planning to solo those.
Level 15-Level 18: A lot of people will be asking you to party at this point, it is only natural since that is the logic in almost all mmorpgs.
Level 19-Level 20: Velpist or Prokeon is a smart choice. No further explanations will be needed for that part.