I have made a large number of scrappy quilts. This seems to be to be the most versitile method. It is possible to do it without a foundation, but it is much more work. Any foundation will do. I like to use batting scraps. Others in my guild use paper (which needs to be removed) or cheap, prewashed muslin. You can use orphan blocks, paper piecing errors, and just plain scrap. A block may have a theme, or common colors, or not. However you do it, have fun. It will go very quickly.
I try to start with a non-rectanglar piece in (sorta) the middle of my foundation. I generally try NOT to have everything I add be a rectangle.
Put 1st 2 pieces on foundation
Open and Finger press
Add additonal pieces.