I am breaking in the air compressor and stapler on The Office Chair. When I worked on this on Saturday, I found it easier if I thought of the project in steps. Hope this helps you.
1. Measure your foam.
I bought a pre-cut piece. DIY Upholstery Supply recommends cutting the foam to 3/4 in. from the seat. As you can see, I did not have that much in some areas.
2. Curt the foam.
Recommended cutting devices are electric knives or a professional foam cutting knife. I decided that I have spent enough money for now so I used a razor blade and scissors. I cut into the side of the foam, about 1/3 of the way down. Then I used the scissors to cut the top 1/3 and repeated the process again.
3. Thin your foam.
I discovered my foam was a little to thick (3 in.) so I peeled a layer off of it. Just dig in and pull off the top, you don’t need to cut. The foam separates easily.
I stapled in the middle of all sides first and then proceeded to continue around the perimeter.
5. Cut batting.
I used batting because that is all I could find. DIY Upholstery recommends 3/4 in. dacron. I cut three layers of the batting to try and make it thick enough to cover the divots created from the stapling.
6. Staple batting.
I found that my stapling was more even if I pulled and smoothed with my palm and all finger tips rather than using only my thumb and forefinger.
7. As before, staple the centers first.
8. Finish with the corners.
I have not found a real hard rule on stapling the corners of the dacron/batting so this is what I did. I recommend stapling in the center of your corner and then adding staples on either side of the center staple.
9. Finally, cut off the excess.
Padding down, upholstery to go.