On the last two Covered With Love blankets I had joined blocks with a simple crochet stitch that resulted in a raised ridge. For this one I wanted to keep things flat so I have used a zig-zag of single-stitches. It's working very well.
To keep everything fairly straight I left the blocks laying flat on my kitchen table rather than taking them in my lap so bending over the project is my biggest problem due to degenerative disk issues, so things are taking longer than I'd like. I have to work in short time increments, but gradually it's coming together.