From my experience it usually goes a bit like this:
- First you need good idea and plot for the quest, this includes the main plot, all different mobs, how the quest should proceed, what are the plot twists and what is the outcome. Naturally the more complex the idea and plot the harder it is to come up with.
- Then you need to plan out how the players will execute the quest in practice, it's not enough if you have a perfect quest on paper, if it doesn't work in practice then you're screwed. This is the hardest part.
- Manually adjust the mobs, give them correct skills, give them nice names, colors etc. and make sure they are the right strength. Place the traps, teleports, gates etc.
- Now you're finally getting close to launching the quest. You'll receive shitload of GM pages "WHERE IS THE QUEST??" while you're trying to setup the quest and monsters and supervise that not only there is enough monsters but also that players are behaving and moving forward as planned.
- 30 minutes from the quest starting you already have to be saving someones stuff from a monster or have complains from players of someone looting or using veritas or mass dmg spells. Meanwhile the other quest attenders are sending you GM pages "WHAT TO DO NEXT? "WHAT NOW??" because they have killed all the monsters already.
- 2 hour form the quest starting, you get frustrated messages and pages how boring the quest is.
- Finally the quest is over and at this point you just want everything to be over soon meanwhile reading the angry pages "WHERES MY QUEST DEED???".