Not sure if this should go into restoration or tech, so I put it here.
The driverrs seat foam in my 86 had taken on a permanent sag due to age and wear. I bought a formed replacement foam from Corvette America but I will touch on that shortly. The seat covering is in pretty good shape for the age so I reused that. Before I started I talked to an upholstery shop about having them do it: $145 and a day to take the cover off one seat cushion and put it onto the other. I decided I can try it myself for that.
In addition to the foam and hog rings I picked up a hog ring pliers at the same time, not really worth the money. I went to Fleetfarm (farm supply store) and they had a LME brand that I bought, works pretty good.
I took pictures of how it was set up, but what I didn't do was compare the 2 sets of foam. Best I can figure, looks like the replacement is a little different and did cause some issues later on.
Now for the real tip. I had a couple of false starts, things just didn't want to go together right. After starting over I had the brainstorm that solved the issues: do the center depression first, then the area between the wings and the main cushion, then the front, the sides and finally the back.
Unless I pulled the seat cover down into the middle of the seat and fastened it first, you can't get that to line up if you start anywhere else. Same with the area between the main section of the seat and the wings, don't have them done first and never will get them down if you have other areas fastened first. Once those are done, then start at the front, get that pulled down, taut and smooth and fasten it. Next the sides and finally the back.
I had some issues with the foam itself as I think there were some differences between the original and replacement. If I had trimmed the new to match the old it might have been easier to get the cover on, but I eventually did.
Hope that helps someone else down the road It was a bear for me till I figured out the order to do it in.

Great tip.