You can only share with party members
Party members must be nearby when you share
Party members must meet the pre-requisites of the quest itselfFor example, if you are on step 2 of a quest and your friend is still on step 1, you could not give him a "short-cut" to step 2
Quests generated from items cannot be shared
Party Quest Share Information
If you mouse over a quest that multiple party members have, it will display a mouseover tooltip indicating what nearby party member are on that questAlso, to the left of the quest name in your quest log it will list a number in parenthesis indicating how many other players in your party have that quest
Quest Text Speed
You can disable the slow scrolling of text when you are receiving a new quest