There are two ways you can attach the solid pieces. The first method would be to cut 12 blocks from your solid fabric, each 12.5" square. These would be attached as you would any basic block quilt. You can sew the blocks together by row or by column. Press, and then sew each row or column together. Press.
If you are using straight line quilting, this method would provide some structure for you to follow because you would have some built in lines to help guide you. If you are a free motion quilter, it might help you visualize the quilt in sections as I know some free motion quilters do (i.e., Leah Day). Something to think about.
The second option for attaching the solid pieces is to measure out the blocks needed to insert in each area and sew in each large piece. When sewing the pieces together, you can either choose to sew the pieces together by rows or by columns. I sewed mine by rows.
(The measurements given are approximate. These are based on IF your blocks came out 12.5" square.)
This will not give you lines to follow and may allow you a looser, more "go with the flow" manner in which to quilt. If you are straight line stitching, you may use tools like an Ink B Gone pen or painter's tape to provide your lines to guide you for your design. We'll get more into that when we discuss machine quilting.
Once you've decided how you're going to attach your solid fabric, it's time to get started putting your quilt together. As I said, I chose to sew mine together by rows so I will give you an idea of how that is done.
Since I took a pledge to post about my progress no matter what, I will say that I did make a pretty big boo-boo. I undoubtedly cut my biggest piece of fabric about 1/2" short and did not have a big enough piece to replace it with. It's close to the edge and I am planning on straight line stitching anyway since I haven't gotten the hang of FMQ yet so I am just going to use it as my first line on the right side. Here is my completed quilt top.
I've got to get some better lighting in my sewing room! Here is a close-up of the blocks.
Happy quilting! And don't forget to show your progress in the flickr group!