Tips to making a good quest:

[AmazingAmpharos]

I find making the last dungeon the hardest one keeps it interesting more than just using a plot twist.

[bob1000]

Back to the boomerang, I have a few ideas if you're using 2.5:
*Before placing an enemy type for the first time, check "Damaged by Power 0 Boomerang/Hookshot" on that enemy. Time-consuming, but if you're adding a sort of "saber throw" to your quest, it works. If you use this idea, make sure to add attack power to the boomerang.
*Make the boomerang cost magic. It will make you think twice before using it.

Also, on bosses:
*Use an Aquamentus as a sub-boss for Level 1(you get the dungeon item when you kill it).
*Custom boss for beginners: Early in the game, use a common enemy found later in the game (like a Wizzrobe) and put it on several screens.

EDIT: I read that using a powerful enemy early on caused problems with people in one quest. To avoid these problems, try giving Link the white sword early or reducing the enemy's attack power.

[Santano64neo]

Also, avoid story lines where you have to re-create a certain overworld over and over again. I tryed that once and as a rookie, ended up putting off the quest. Now I'm creating one with a bit of a plot(eg. an actual reason for collecting the "Triforce") while making the overworld a bit more scattered.
It saves time on re-building overworlds and you don't have to worry about a "What if the player gets that heart piece and the one I'm using in the re-created overworld?"

[Din]

Storyline: Not the usual "Hey, let's save Zelda for the nine hundred septillionth time!" A good story makes use of plot twists, and giving an actual cause for fighting. Hero of Dreams was a great example of this.

Bosses: It may take a lot of time to make custom bosses, but it's worth it. Good bosses punish the player for mistakes, but allow the player to learn what they did and come back for more. Plus, add in a fun factor, and decent music and arena, and voila!

Difficulty: Now, a good quest should start out very easily and give a player a chance to learn the basic controls, perhaps starting out with a dungeon to proceed in the quest, and fairly easy so it doesn't kill the player. Meanwhile, later on, the dungeons slowly get more challenging, but not completely exceeding their skill level thus far.

Sword: Okay, we all know how valuable the sword is, but make the player work for it! Perhaps start out the player with low ability, giving them items that are hard to kill enemies with, such as the boomerang and the candle. Then, when the player finally gets their sword, they realize that they are pretty much okay without it. Although I don't need the sword, there are many players who do. So, perhaps have a "Hero's Cave" style dungeon, in which the reward at the end is a sword.

Extra Dungeons: Easily what keeps the player coming back to the dungeon. Make decent extra dungeons by adding GTL. These would be Gimmick, Time, and Layout.

[Shazza Dani]

Sword: Okay, we all know how valuable the sword is, but make the player work for it! Perhaps start out the player with low ability, giving them items that are hard to kill enemies with, such as the boomerang and the candle. Then, when the player finally gets their sword, they realize that they are pretty much okay without it. Although I don't need the sword, there are many players who do. So, perhaps have a "Hero's Cave" style dungeon, in which the reward at the end is a sword.

This is the worst idea ever. You see it in so many quests, and it's so irritating to fight enemies without the sword. Especially when you have the Boomerang and the only enemies you can kill are Gels and Keese, because those enemies can never drop hearts. And making the player fight Bats is just cruel.

Not to mention giving the player the Boomerang from the very start is foolish, because stunning enemies makes combat so easy once you actually have a sword—you should have to wait at least a little while before getting the Boomerang in a quest.

As for the Candle, it's arguably more effective in battle than the sword if it doesn't require magic, and it's also a common item to trigger secrets, so why give it away at the beginning?

[DarkFlameWolf]

Or you could do like Lost Isle with the 'no sword in beginning' and only set it away from the player by about 4-5 screens. So he stumbles across it early in the quest.

[Moo2wo]

A tip from me is try not to use graphics that are better than the game. While appearence is important, having a solid, enjoyable, bug-free quest is more important. Look at End of Time! It uses the most basic tileset (classic with LttP Lava) and it's my personal favorite.

[Orithan]

1> YEAR BUMP! (I hope I didn't Gravedig)

I may be a newbie, but here's a good suggestion, try to create dungeons that have an unusal characteristic to give them that added flair, like for example, a dungeon with water on one half and with lava on the other like in Link's Birthday, but with the trait of switching the two enviroments around via central switch, make flooded ares filled with lava and vice versa, make some burning tiles cooler and warm up freezing tiles to make paths, also change the enemy sets around for those areas when you flip the switch, and of course, make the changes reversible when you hit the switch again, like for example, you want reach a speific key that's surronded by burning-hot tiles, flip that switch, and those burning-hot tiles are gone, so you can acess the key, but what if you wanted go through a door and now the waterfall over it is now frozen, just flip the switch again and presto! The dungeon is back to normal, save for the key you just got. I think a similar thing is being implented in Neofirst.

Other elaborate additions to dungeons:

A maze where if you take a wrong turn, you either die or go back to the entrance.
A darkened dungeon when you go a little bit into it, you get chased by monsters untill the end of the dungeon, that kill you in just one hit.
You can only access the boss if you have a speific person following you around and you enter the boss room with him/her (Blind in LttP).
You can rotate the between four seasons so you can get to certain areas of the dungeon in one season you couldn't in the other.
You can go from the interior to the exterior of the dungeon (TP's Snowpeak Ruins).
Guards that throw you into jail if they see you (Shoelace's Hero of Dreams, Fort Wolfblin).

That the all I can think of right now. If theres any more, I'll be working on a Super Metroid hack tonight because Zquest 2.5 betas won't work on my laptop but ZC does, and I will have acess to a computer that loads it on Friday to Sunday. Ciao!

Edit: Whoops! I forgot to add someting.