Since this is a roguelike setting, unlike "set in stone" games like Skyrim, you may also want to consider the possibility of quests that are (or eventually become) impossible: it's the player's responsibility to determine if the quest is worth doing or if it's even doable at all. This lets you hand out quests that have a time limit, or require things of a player that cannot be done without assistance (such as NPC tag-alongs), or simple aren't feasible unless some random event allows the player an exclusive chance.
An example of the last case would be along the lines of destroying/conquering a town. By yourself, or even with a small band of helpers, this is very likely an insurmountable task, but if there just happens to be a horde of monsters rampaging its way through the area, and they just happen to cross paths with that town, then you could use the opportunity to seize control or set off some well-placed explosives or any number of contingencies set up in wait for a fortunate event.
I suppose the ideal is that you give the player a lot of ways to solve problems, and then you hand out quests that have amorphous solutions and ramifications to them. If the player is told to assassinate a political figure, they better do it either stealthily or have an escape plan, lest the consequences of such actions cause an unexpected demise (at least unexpected from their perspective). Perhaps you may also want to add "context" to the quest-givers: someone asking the player to "kill X many of Y" could very well have a motive, if the only Ys in the area are on private property, or are a rare species, etc.
Generally speaking, however, I'd suggest building up the environment with which the player can interact, then figure out just how creative you can get with the quests based on what you have. With any luck, a robust enough world will practically write the quests for you!