Hi BorntoQuilt,
For a good planned scrappy, you can pick out a quilt block that has a fair amount of pieces in it. You decide that one component of the block - like star points- will be from one color family. You also decide that another component - like the background in each block - will be from another color family.
In Pulsar, my star points were dark blues and purples. My background was cream (6 or 7 different cream fabrics).
I knew how many blocks I needed and how big each piece needed to be, so I could generally figure out if I had enough blue and enough cream before I got started.
My method for picking out all the rest of the fabrics was this: put them on the floor in a random way. Put some of your darks and lights (previously chosen) with them. Stand on a step-stool, sturdy chair, or go up two or three stairs. My sewing room is at the bottom of a well-lit stairway. The base of the staircase has been the stage for auditioning many fabrics for many quilts. You may not know what you like to start with, but you will see right away the fabrics that don't work or play nicely together. This distance of more than your height helps to see the fabrics in a different way. You want some blending and a little contrast. If you like how a certain color looks, add more of that color in different shades.
I hope that helps. pm me at any time!