A couple of years ago when I 'discovered' this technique, I thought it was the greatest thing I ever thought of, until I saw it in a sewing book. I wasn't disappointed to learn that I wasn't the first to ever try this, but more like relieved that the pressure of announcing a new technique to the world, would not be on my shoulders :D
Rotary Cutter & Mat (optional)
Mark lines in 1 1/4" increments using a chalk wheel marker and ruler. Be sure that the lines are exactly spaced, each time.
Now you're ready to sew and pleat your fabric. Fold on each line and sew at 1/4" on each fold. Press the pleats going all in the same direction.
After the folds have been pressed in the same direction, turn the fabric and mark line placement at a minimum spacing of 1" each. Once the markings are drawn, you will be able to follow along that same line as your sewing line, alternating the pleats in 2 different directions.
Sew 'down' the flat pleat sewing line first. Turn the fabric and sew 'up', flipping the pleats and creating the 'wave' look. Try to keep the sewing lines as straight as possible.
Once you've completed this process, your piece should look like this..
Here is what I used my mexican pleating patches in..