Here are some of my random scrappy blocks. I just start sewing pieces together. Then press and trim so all sides are straight. Sew some more, press and trim until they're a bit bigger than the size block I want. Then trim to size. My blocks are 8-1/2 inches because I have a ruler that size which makes for easy squaring up. One thing I've learned with this technique - starch is your best friend. With all those random seams going every which way it really helps.