Right now Craftsy has a free class on color usage you can take, also. I just signed up for it last week.
My stash has really grown because I buy lots of clothing, linens, etc. to deconstruct from thrift stores. As long as they are cotton, I'm good to go! Also, I sort my stash by color.
What works best for me is picking the focus fabric and then finding things to go with it. After I have a pile of fabrics that I like together.... I often pick as many as 10 or 12, then I look for a pattern. Once I find a pattern, then I fine-tune my fabric stack to suit the pattern needs.
A really fun thing I do sometimes is set the timer for 30 minutes and see how many sets of fabrics I can pull. By doing that, I improve my color picking skills. Making those snap decisions is good because it keeps me from thinking about it too long so sharpens my eye.