I did a road trip to South Carolina about 6 months ago and found 5 dining room chairs at an estate sale, did some stellar negotiating and got 5 mid century dining chairs for $100. It was such a score, until we got home and saw that 3 of the 5 had cracks in the wood. I was super bummed but decided the other two would still work out. I went to Hobby Lobby and bought 3 yards of fabric, 1" thick seat foam from Wal-Mart and batting. Last but not least I snagged a can of spray adhesive after I reviewed a check list I found online about how to actually upholster seats. I had previously bought a heavy duty stapler and staples so I was all set.
I plucked out all the old staples (and then removed the old fabric and batting) with pliers and a flat head screw driver. This took about a whole day to complete all 5 chairs. I was proud of the work and happy that step was over, sore hands and all. Then a few days later, during a good baby nap I started to put it all together with the fabric. First, cut the foam to fit the wood, and then lay the fabric out leaving a 3" overhang so there is room to staple it down. You need to spray the wood with the spray adhesive so the foam sticks to the wood and won't slide around under the fabric. Next, lay the batting over the foam (sprayed the foam) and then place the fabric over the batting so your pattern is in the position you want it. I laid this all out on the floor first and then flipped it over to check my pattern. Pull all the corners in and staple them first. The sides all get pulled tight and stapled after that.
Here is what I came up with...