The first post-planning step in weaving is to make a warp, or a collection of threads into which the weft will be woven. These can be all one color, many colors, or a repeating pattern of two or three colors, but they need to be the same length and they are often quite long.
The easiest way to create a warp is to use a contraption called a warping board that allows string to be wound around a series of pegs. My first couple of warps were wound on the warping board of my co-worker who taught me how to get started, but if I was too impatient to wait until I could go over to her house I would create a warp using a combination of dining-room chairs and pegs clamped to tables. That gets rather tedious when I need 400+ ends that are about 5 yards long.
My first unemployment project was to make a warping board for myself. I used this pattern from All Fiber Arts:
http://www.allfiberarts.com/library/graphics/gallery/wrpbrd_pln.gif. It's a bit hard to read, but the pattern was good enough. I modified it slightly (of course) because I don't see myself ever needing a 16-yard warp.
Here's the end result! It's not beautiful, but it works.