Concentrating on yellow quests will mean you are receiving enough power leveling experience points for your efforts, and that the region in which you are questing is at an appropriate difficulty level. The only enemies worth killing are yellow and above, and green enemies, while easy to kill by the dozens, often provide few experience points, and loot that is often less than your needs. Certain classes, and certain players, can pull off the occasional orange or red kill, but they take a long time and the payoffs are not as much as you would expect in terms of experience. These kills may have better item drops.

 

Likewise, concentrate on yellow and above quests for power leveling, and abandon greyed out quests every time you level. It may seem like the items or payoffs from these quests make them worth hanging on to, but when you are trying to get your character to level 60+ in a hurry, wasting time to complete these power leveling quests will detract from your time spent cleaning up on experience points and loot. Areas that look like farmlands, typically populated by Gnoll, Undead, and Human enemies, are often the focus/center of quests involving theft, revenge, or destruction. Whenever you see a farm, stick around for a while and kill the enemies which populate the farmland as they repop.

 

Typically, these areas will also be a good place to come back and farm, especially later in the game when farming becomes critical to finishing up your character's gearing and advancement. As long as the enemies you are killing are yellow level, they will be a good source of quick experience and loot. As they repop, knock them down until your bags are full and you are becoming bored with killing, then finish the quest up and move on. Remember the farms whenever you are short on cash and need loot fast. And farming while questing will fill your bags with loot, and give your power leveling experience a boost.