I was playing on a server, and I was just recently given a quest. The previous quest person handed me the book that had the quest in it. A good way to make the quest interesting is to have some backstory, such as evil wizards, ancient demons, malicious curses, and so on. The backstory is what made the quest fun. This was the quest:
1) Kill a Ghast and collect it's ghast tear
2) Obtain a magma cream (I crafted it from blaze powder and a slime ball)
3) Find a nether fortress
4) Kill a blaze and collect its blaze rod
5) Collect some Nether wart (luckily I had a farm of it)
6) Kill a creeper and collect its gunpowder
7) Make a brewing stand
8) Make a potion of Fire resistance and a potion of regeneration
9) Make them throwable
Notice how all the items I collected worked together to make the potions. This results in a feeling of accomplishment, and makes you feel like all the item collecting wasn't worthless. I was then told to find a jungle and desert temple. The server I was playing on had a live map, so this wasn't as hard as it could be. Otherwise this would be a hard and tedious task, and I would not recommend it. I was told (I haven't gotten this far in the quest yet) that the temples will point the way to the keeper of the books (the wizard that cast the curse that "made" me do the quest). If I were doing this, while the player was raiding the chests, I would put a book in their inventory, one with a X cord, and at the other temple, one with the Y. This obviously requires you to be following them, so the previous quest person was a "guardian" of the quester. I just ended up protecting the guardian, though
When the character got to the location, you would probably have built some sort of temple previously, and another player (or yourself) would be the wizard inside. In my quest I was instructed to throw the potions at the wizard. I was also told I would be rewarded with diamonds XD. After someone completes a quest, reward them or they will get mad. Then, give them the book and tell them in order to fully complete the quest (or lift the curse, and so on) they must pass the book to a new owner, and be their guardian, or maybe the new quester would have to guard them. This results in quests being constantly passed on, so multiple people can have fun with it.
I hope this helps in your quest-making!