Here is my version of a ruched pillow. I wanted something with lines in it, I think it turned out cute. Feel free to use this tutorial for personal use. Thanks.
1. First you need to cut out your fabric. Cut out 2 squares of fabric to fit your pillow form or desired size. Remember to cut your fabric to the size of your form or slightly smaller to have nice full pillow. The third piece of fabric you cut out needs to be your pillow size in one direction and 2X the length of the other side. Mine was a rectangle (18X36).
2. Next you will need to mark the lines you want to gather on with a fabric marking pen or chalk or something. (I pieced my tops together because I was using leftover scraps of white muslin).
3. You need to mark the center of your pillow at the edges and at your marked lines. Also mark the center of one of your square piece of fabrics.
4. You need to sew a gathering thread. Use your longest stitch and stitch the top edges, bottom edge and your 2 marked lines, be sure to leave long tails. (You are not sewing anything together, you only have the one piece of fabric).
5. Now you will line up your centers of your extra long piece and the other pillow square you marked the center on.
6. Pin your extra long piece to the square piece at the edges and the centers. This is 4 pins on each edges and down the center, you have pinned in 12 places.
7. Start pulling your gathering thread. Pull until the top (gathered) piece of fabric is now the same width as the underneath piece of fabric. Repeat for each line. I like to work on one half at a time. I pull from the left until the left side is all nice and ruched and then I work from the right.
8. Pin your fabric the underneath piece of fabric. Be sure to keep your top piece pulled tight, make sure you line stays straight.
9. I used a lot of pins.
10. If you are adding any trim add it now. Pin the trim on top of your line. Again, make sure you keep your lines straight.
11. Sew on the top edge, you lines (or on top of your trim), and the bottom edge. Sew nice and straight - take your time - you don't want to unpick. Now your ruching can't move around on you.
12. Pin the remaining square to the top of your ruched pillow piece (right sides together). Sew around the edge, be sure to leave an opening wide enough for your form to get through.
I like to round my corners, if you do this is the time to do it.
13. Turn your pillow right side out. (I dyed mine a blueish grey to match my living room). Stuff it and hand sew the opening closed.