Carol Doak has an awesome explanation/video in her 50 pp'ed stars book (it's a DVD). It may be on her website too. I bought an "add a quarter [inch] ruler) and boy does it help. I got the longer one so I could do bigger blocks. It involves using a postcard fold the paper over and then placing the ruler on it to cut the quarter inch. I am sure you could do it with any ruler but the add a quarter ruler and Carol Doak method makes it so fast.
Night and day difference from my first set of blocks that were so bulky. I LOVE the look of pp'ing. Hope this helps.