I think the key is to answer what type of quilts do you like to make. Do you like to use patterns with specific sizes, ie 5" squares, layer cakes? Do you like string or crumb quilts, where any width and length works? As mentioned, Scrap Therapy and Bonnie Hunter's system works for some...do you like the quilts that are made from these methods? Kitsie makes adorable 6" blocks all the time (we never tire of seeing them, K!)
Once you have figured it out then start cutting some scraps to see if it really works for you.
Personally, I am overwhelmed with scraps...mostly everyone else's...that I am just cutting a bunch of them in the biggest size and work down similar to BH. I also make miniatures so for me...nothing's too small...well almost nothing!