I have made a few scrappy quilts and what I have learned from them is that the more different scraps used the better.
If I use only a few different scraps I end up with color blocks instead of a scrappy look. The more the merrier.
You have to stand back and look at the quilt as it grows. Some colors may not look good right next to each other but if you separate the " offenders" by at least three places they become good friends.
Try taking fifteen 3" squares picked randomly out of a bag. Line them up with no space in between them and in no particular order. Now re arrange them into 4 patches so that most of them look nice next to each other. peach and green look great next to each other, teal and orange, purple and anything, just play with them and they will each find a good friend to live next to. In a whole scrappy quilt they all blend together
Remember the whole of what you are doing. A scrappy quilt almost never looks good with only a few blocks done. The more you add to it the better they get.
If you are making a small wall hanging build many small blocks instead of a few larger ones. Anything goes in a large quilt.
Scrappy quilts are a lot like stew, it's only good after all the ingredients are added.
Play with your scraps!
peace