Start stapling! You will need to use a heavy duty staple gun. I stapled following the order of the numbers in the photo below. Every time I stapled, I made sure to smooth out the fabric and pull it tight. That’s why you always staple one side, then go directly across from it next… it helps pull the fabric tight.
After you’ve stapled a lot, you’ll end up with bunches of fabric that stick up. Pinch them into triangle shaped pleats like this:
Then staple them in three places, like this:
Continue around the whole circle until everything is stapled down nice and tight.
You should be left with a perfectly reupholstered seat cushion!