One of the problems I had when starting (and still do at times) is the ruler slipping. Those sandpaper dots help with that. Also, most of the tutes will give suggestions on how to hold the ruler so it doesn't slip. I've seen several suggestions so you just need to try them and see what works for you. As others have said, practice on old sheets or something similar. Then check to see if your cuts are straight and the strips are uniform width.