Ok so this takes, well, 2 people, and requires you having a level 50 disciple of war/magic for it to work.
Levequests break crafting. I'll explain:
In order to get Leves you have to initially do a combat oriented leve, to be able to access the other leves, hence the requirement of a level 50 DoW/M (well maybe not 50 but you'll get the point...).
Each Leve, which range from level 1~45 ask for you to craft different items. However, it doesn't register completion by the act of crafting, rather it counts as long as you have the requested item in your inventory (and not bound iirc). Because of this you can have a 2nd person craft all of your levequest items. As a level 50 crafter can 100% HQ most items all the way to at least 30~ish level recipes, you might realize where this is going.
@nd person HQ's all your levequest items, trades them to you, and you turn them in. Since they are HQ, guess what you gex 3x the normal xp. For example, a level 15 levequest will net you 18k a piece, 10 hq cotton halfgloves and bam 180k xp in about 2 minutes, the time it takes to accept and turn in the quest 10 times.
The only thing that limits this no-effort crafting powerleveling method is the number of Leve allowances you have available.
As this is, in my personal opinion, a borderline exploit, I can't guaentee SE won't end up taking action against this. I do believe that they will most likely address it in some way, such as, requiring the action of crafting the item to trigger quest completion, however at that point it may still only need the motion of synthing an NQ item and swapping it with an HQ in your inventory. So...I don't know.