Questing is a great way to level because you get guaranteed rewards after the quest(s) are complete. This helps because one may have an item you wish to obtain, or maybe you just enjoy the story line associated with the quests. This is by far one of the most popular ways to level up.
The problem with questing comes in after you run into an area with many others working on the same quests. Many times you will run into other players who need the same mob as you do, the same quest items, etc. and do not wish to share.
The game does have a system set up for players who wish to quest with other players, however many people would rather go solo (at least at the lower levels) due to wishing to complete their levels as fast as possible.
If you do wish to group with others and they agree, items will be shared on a 50/50 basis (assuming there are two players, 33/33/34 basis with three, etc.). This makes everything go very smooth when questing because it allows all players to be finished within one mob of each other.
An example to better illustrate this is if you have two players who each need 5 items from Mob A. You are both grouped and so you assist each other on killing Mob A to speed up the killing process. Player 1 gets the first item, Player 2 gets the second item, Player 3 gets the third item, and on until everyone has all of their quests items.
The reason this system works exceptionally well is because it keeps one player from “ninja stealing” off everyone else’s work and then moving on without them. With this system in place it helps keep everything organized, friendly, and smooth.
But this is also the system’s downfall. Once you get to an area with people who do not wish to share their quest items, you will be forced to either compete with them for the quest mobs or you will have to just sit back and allow them to complete their quest first.
As a personal recommendation, in cases like this it is best to take a small break (say for a drink of water, or to use the restroom) while you wait for them to finish their quest. This helps everything run much smoother because it keeps one player from getting aggravated and griefing another.