I write down every size piece and how many of each as well as each color. I place a straight pin with a letter glued to it and mark it on my piece of paper. I find those clips that came out awhile back hold my pieces together nicely. If I have too many pieces, then I place them in a plastic bag. I have 2 drawers full of small plastic bags in all sizes for this idea. The straight pins with letters glued on them were made using Elmer's glue, baby beads from Walmart and straight pins with the yellow ball on their ends. I made 7-10 sets of them so I always have enough of the 1st 15 letters as it seems I'm always using them.
Also once I've cut my strips, then subcut, I mark it on my piece of paper so I know I'm done with that step. I also cut my sashings, borders and bindings at the beginning and marked that I've done it. Forgot to cut the strips for the binding once and when I finally got to the point of putting the binding on, I no longer had any of the fabrics used in the quilt. I keep all my bindings wrapped on TP cardboards, marked for which quilt it's for and then placed in a container with other bindings waiting to be used. My sister says I'm OCD but I prefer being as organized as possible.