simple seat cushion cover

This is what it looks like now. To make it a little easier on myself, and not mess with all the foam cutting-I bought a chair pad on clearance. I matched up my print so that where the seam met, the rows wouldn't be mismatched. Again, I'm not one to measure, so I just guessed and left about an inch extra all around to account for 1/2 inch seams.

Next, I cut 2-inch wide strips for the ties that hold it to the chair. It doesn't really matter how long you want them, that's up to you.

To sew the ties, I hemmed each end of the strip. Then, I sewed them up just like you make double bias tape, and stitched as close to one edge as I could to finish.
They'll end up looking kinda like this, and they will probably twist on you too:

Before you attach the ties to each piece of the seat cover, do a rolled hem on the side that would be the BACK of the cover, where it will rest against the back of your chair.
Next, attach the ties to each using a pin and zig-zag to the panel. I don't have a picture for this, but you can see how that looks in the next pic. Next, you want to pin the panels RIGHT SIDES TOGETHER, making sure that the hemmed edges are as closely lined up as you can. Depending how much of a perfectionist you are when you cut (I am not), they might be a little off. I didn't care too much, since this is the back, and not visible unless someone is seriously looking at it.
Here they are pinned together.

Sew up 3 sides only, leaving the side where you attached the straps open. Pull the pins out, and turn. Make sure you trim off all the hanging threads.
Put the cushion in and tie it to the chair!