This of course does not require any [Sub] quest to be completed. All you have to do is make sure you do all your Main Quests.
If your not Level 65 yet.
I suggest buying Vitality twice a day. (Anymore and the cost raises by 40 which is not worth it unless you have the wallet/purse for it)
Skip Trail Tower and use it to grind on the highest level mob you can fight.
Do all the daily Events for the EXP.
Try to maximize your slaves EXP.