Draw Maps and Floor Plans
The maps and floor plans are for reference only, so they just need to be rough sketches. Sometimes I draw them on paper and scan them onto the computer, and other times I just use a paint program (I like Paint.NET because it's easy to use, but still has a lot of versatility...and it's free).
I start by making a list of all the places my characters go to, including cities, towns, islands, etc. I also make a list of buildings they go into.
Then I make a map of the world/island/nation/city where the story takes place. For instance, my Shadow Stalker serial takes place in two main locations: the Serpent Isles (which is a chain of islands in the shape of a serpent, hence the name) and the Dark Isle. So I start by drawing maps of those places, including terrain, cities, towns, etc., or in the case of the Serpent Isles, I will label each island. I also make notes of how big those places are and the distance between the islands, and the paths travelled by the characters on each of the maps as I draw them.
If the story takes place in a larger area where the characters travel to different places, I make individual maps of those places as well. For instance, I will draw maps of the villages on the Dark Isle, and I will also draw the islands in the Serpent Isles where my characters travel. Then I will draw maps of the cities, towns and villages they visit on those islands as well. The cities, towns, and villages will have buildings, streets and other landmarks labelled.
Finally, I draw floor plans for any of the buildings my characters go into. If a building has multiple floors (like a high-rise), I only draw floor plans for the floors my characters visit.
Then I go back and, using the maps and floor plans, I determine how long it would take to travel to the different places based on the distance and means of travel. I also figure out how long it might take to walk through certain buildings if time is a factor in the scene. I make notes of this in each scene, and I also make adjustments to the timeline and move scenes around if necessary.
Again, I feel it's better to work this stuff out before I start writing, so I don't end up needing to rewrite things later. It saves so much time.