I lay my fabrics on the end of one of the tables in my sewing room. I often leave them there while I'm working on other projects so that I look at them often. If something looks off, I pull it out and see how the other fabrics look. I often do this for a period of weeksm adding and subtracting fabrics. When I think I have the combination down, I take pics, turn them black and white and then make my final selection.
Of course, sometimes I'm not that scientific. Some times I put the fabrics I've chosen down and stand on my sewing table and pull other fabrics from the boxes on the shelves on the wall and drop them on the other fabrics. From 5'4" away things that work and don't often show up. I know it sounds humorous, but it's worked more than once for me when I was stuck on what to add to a particular group of fabrics.