Step 1: Make a model
When I had to move all of my stuff out of my old place to my new place I became somewhat concerned as to where I should put everything. I really did not want to have to move things around too many times. Most of my stuff is heavy, some weighs upwards of a half a ton. So I knew what I had, and I knew where it all had to fit, so I made a model of it all.
The first time I was exposed to this idea in a book I laughed at the fellow doing it. When it came my turn to setup a new shop it didn't seem so funny after all. It is way easier to move little cardboard models around than full sized objects! Oh, and for all you graph paper cutout types out there it is far too easy to lie in 2D. I have gone the graph paper/cutout route before. That has never struck me as being very silly, just not as effective.
I used the architectural scale 1/4 inch to the foot as my scale. Heck, after a while it was sort of fun to make scale models of all of my junk. In the process I even remade a few of the models nicer than I had initially. The models are made out of scrap cardboard, and toothpicks, hotglued together, then painted with craft paint. Nothing too fancy there. But everything is to scale.
See the little scale me in the model? It was a handy visual aid for me to see height relationships, or how I'd fit in the environment. OK maybe the minime was going a bit too far? All I wanted was sharks with laser beams, whoah wait a minute. That is another story.