Here is a tutorial for making the striped blocks I've been posting about recently.
In this tutorial, for every two nine-inch squares cut from your striped fabric, you will have two squares at the end, like the ones above, one with four pieces, and one with eight pieces.
Caution: this post has about 40 photos, so if it's taking forever to load on your browser, that's probably why. Also, I'm left-handed so if you see how I've ironed or cut things and it seems a little off to you (and you're not left-handed), that's probably why. Just do things on the opposite side of what you see in the photos and you'll probably be fine.
First, find some striped fabrics that you like. Some of the stripes that I have were fat quarters (the fabric piece is about 18"x22") and others were "long" quarters, i.e. regular quarter-yard cuts, which should be a little bit more than 9" if the quilt shop that did the cutting was conscientious and/or generous. In some cases I have quarter-yard cuts that are exactly 9" down by the selvages but then narrow to ~8" at the fold because the cutter was not paying attention to the details.
Press out any wrinkles with an iron, then line up the stripes on the cutting mat. Generally the stripes will run either parallel to the selvage or perpendicular to it. You are going to cut nine-inch squares. I find it easiest to start by cutting parallel to a stripe if possible. Line up the stripe on the cutting mat and cut a nine-inch strip.
Then cut the middle squares in half, making sure to cut parallel to the stripe, not perpendicular. For the square to look the way it does by the end, this is really important. If you mess up, just put the pieces in the scrap pile and start over. After you finish this step, you have all the pieces you need to begin sewing.
Because this fat quarter wasn't necessarily cut keeping the stripes in mind, I made sure that my triangles would be true to the stripe by lining up a pre-drawn diagonal line on my cutting mat (I used a sharpie marker) with the length of one of the stripes. If you look closely you can see that (there are also pre-printed diagonals on most mats - you can use the one that says 45 degrees - in my case I drew one that ran in the opposite direction of the pre-printed ones - it was left over from a project from several years ago when I was squaring up blocks for Izabella's Puzzle).
this link to Wikipedia). And four have the stripes running in a different direction relative to the hypotenuse. So four of the triangles can be made by cutting another 6.36" square from the diagonally-striped fabric. Cut the square, then cut on the diagonal and again on the opposite diagonal, like this: