How to come up with quests.

I find it easier to start with the map editor's capabilities. In most cases, the quest mechanics are conceived first, and then the story is developed around them. When I discovered that the size of static objects could be changed, I immediately came up with a quest where you had to find a couple of huge Christmas trees and figure out their secret. After finding a bunch of unused trees among the hidden objects in the editor, I created a quest where you had to search the map for unusual plants. Seeing that the illumination of objects could be turned on and off dynamically, I built a quest around turning off the lighting in one of the locations. The ability to create and delete static objects on the fly gave me ideas for a whole series of quests where you had to destroy or move something. Or, for example, a standard type of quest where you have to bring something. In the fifth game, this could be artifacts, resources, or creatures (as well as "virtual" objects that won't be visible in the interface, but their presence can be emulated with scripts). Learning a specific spell can also be considered a variation of the "find and bring" quest. For variety, it's best to use all possible options and their combinations, rather than focusing, for example, only on delivering artifacts.

What principle do you use to distribute them on the map?

As a rule, you can divide the map into a starting location, a middle area, and a high-level final territory. It's best when quests appear evenly throughout the game, rather than all at once. At the beginning, you can give a few small quests for leveling up, as well as a couple of long-term, multi-stage quests that will give the player a direction for development. Instead of aimlessly exploring the map in random directions, the player will rely on the information from these large quests to find out where it is best to advance. The final stretch is the time for serious combat quests, and you can also make the player race around the map for speed, as it is already all open.