First, make a manageably sized drawing, to scale.
Tape together a huuuge piece of paper, the same size as your fabric. Use a ruler to tile it into 1' by 1' squares.
And, square by square, convert your little drawing into a big one.
You can't really see that, can you? Here, I'll Sharpie over my pencil sketch.
Now, what we need is an enormous light box.
Trace. I'm using Pilot Frixion pens here, and so far they seem much more precise and easier to use than the washout fabric markers I'm used to. Thanks to Florence for the tip.
And once you're done tracing on the fabric, the drawing even keeps a little one busy...for about five minutes.