Let me start by saying I have thousands of cut squares, rectangles and triangles.
I cut leftover and fabric I'll never use into squares ranging from 1 1/2" to 6"
They are then sorted.
Most of the 6" squares are novelities and they are just stored in a large box.
A lot of the 4 1/2s and 5s are also novelities and those I sort by type : children, flowers, sports etc.
The 1 1/2"s, 2"s, 2 1/2"s. 3"s and 3 1/2"s are sorted by value: dark, medium and light
Usually I use these in square blocks - how many are in the block depends on the size of the square.
Any block with 16 or more squares always has 3 black squares in it. I learned this from someone on an old Simply Quilts show and it makes a world of difference.