Be especially careful with reds, they can bleed and leave color residue on other fabrics. I wash my reds and purples together but separately from my other fabrics. Again, personal choice here. Do not use fabric softener when pre-washing your quilting fabrics. If you want that soft feeling use softener after you ve made your quilt and are giving it a final laundering.
Fabric softener does just what it s name implies - it softens fabric.
A word about washing small pieces like fat quarters or eighths. I still clip the corners, just smaller than on a longer length, and wash them in a hosiery bag. It gives them a little bit of extra protection and cuts down on the raveling. If it s really hot outside I will line dry my fabrics because the shrinkage factor will have been eliminated in the hot water washing process. I prefer to machine dry flannels and neutrals for that extra step of shrinkage protection.