The first thing I did was to calculate the quilt size that I wanted. I decided to make it a twin, but on the large side so that it would work on a double bed as well. I laid the entire quilt out electronically using MS Paint... it's not the most versatile graphics program, but it was quite adequate for the purpose. I really got waaay into this electronic layout. I went as far as to copy fabric swatches from the site where I purchased the fabric and use them as my building blocks. I tried random distributions and arranged distributions, and various border sizes and compositions:
In the end, I decided to go with the design shown above, center. I liked the random layout, but was afraid it would overwhelm the embroidery squares. For the border, I knew that it needed to be fairly large so that I would not have to make the center larger (and do more embroidery!) I liked the quilted portion of the border, and arranged the rest to be simple, but somewhat broken up so that it didn't attract the eye too fiercely.
From here I calculated the fabric requirements. It took quite some time, and I'm glad that I saved the information, because I have referred back to it several times. I double and triple checked my numbers, (and then quadruple checked because the first 3 times I got a different answer each time... finally figured out that I was treating the borders incorrectly). Even when I got it all straightened out, I ordered extra of everything because the fabric was selling out. I will be glad to have some extra when I am done... it's such cute stuff!