just play and have fun. For four patches...I sometimes just take whatever, sometimes I use two darks and two lights...sometimes if I have a lot of one color but scrappy in nature, I will put two neutrals and say two reds together....hint....if you are planning on have sashing or plain blocks in-between...I helps to know what color you are using ….so say if I were going to put green sashing between the blocks...I probably would avoid putting my green squares in unless of course they were a different value or shade or actually a print....actually, you can not go wrong with scrappy four patches...just put them together and play....