Before you start cutting, you might want to have some patterns in mind and cut accordingly.
I cut a ton of my batiks and also some of my favorite blues/greens/purples into jelly roll strips because I use them most. If I am going to do some D9P's I will cut charm squares in the colors I think I will use. I only cut layer cake squares when I plan to use that size. I do have several projects cut and bagged, ready to grab and sew. Often I get distracted by a new pattern, or new fabric that I just have to use NOW! LOL
As I am cutting other patterns or trimming up the edges after I've quilted something, I try to cut up the leftovers in to whatever usable sizes I can, whether square, rectangle or strips.