I do very very little prep work. Grab the stuff we need, put it on the table and go.
If we’re doing a campaign, we tend to usually know what is going to happen. If not, sketch out the 3 most likely events and roll randomly.
We almost always adapt it to the terrain and miniatures we have available though.
With the people I hang out with, too much prep work = game ends up not happening because someone gets distracted with something else 🙂
Nordic Weasel Games