This is a good tip :D :D
To see what the fabric will look like cut into small squares. Cut out the center of the cardboard or fabric ( needs to be white in order to show up) to the size you need. For example cut a 2" , 4" or whatever size you need.
Take it to the fabric store, and then lay it on the
fabric, what shows through the center is what your squares
will look like.
You can do the same for tru=iangles just cut the size you need.