It took me a bit of courage to just sew and not think about the fabrics.. But the results can be quite wonderful.
I will admit that I collect my scraps and put them into bins, bases on colors and type , blues , browns, batiks and non-batiks etc. And tend to work through a bin at a time, maybe trowing in a few handfuls from other bins to give some extra ..interest. If you look closely at the scrappy quilts you like you will find the reason you like them.. jewel tones, equal amounts of light an dark..etc ... each person has their own taste , you can have it work for you in a scrappy, just do a bit of prethink ... then just do it ! Give one a try !
One tip .. smaller pieces of fabric allow the colors to visually blend together. I don't do scrappy with anything wider than 1 3/4 inch .. and prefer 1 1/2 inch.
Log Cabins are a great first step in scrappy! Just have a bag of light and a seperate bag of dark.