First, lay out the old headliner on the new one and trace the outline on the new one. Mark the center of the front and back for reference by folding the headliner in 1/2. Then, remove the rods one by one and install them in the new headliner, and cut the welting channel so at least 1 1/2” of the rod shows at the end. Use the spray can headliner adhesive and go around the outline you drew on the new headliner, and on the perimeter of the car. A piece of cardboard as a overspray shield will help keep overspray at a minimum.
Then, hook the tension rods to the rear bow and put them in the holes on the back of the window channel and stretch the bows forward one at a time. When you get to the front, use the center mark and line it up with the where the rear view mirror mounts, and hook it there on the teeth. The headliner will be tensioned down the middle, so it’s time to work the headliner out from the middle to the sides, starting with the front header.
Go to one corner and pull the tension tight and secure it on the teeth, the go to the other corner and do the same. One of the tricks I learned is to use some door jamb welting pieces to help hold things in place while you work. Stretch a little, slip a piece of welting on, and work your way towards the center of the front header until the headliner is smooth, and there are no wrinkles between the header and the first bow back.
Then start your way towards the back, over the doors, doing the same thing, pulling tight, but not too tight, and slipping on a piece of welting to hold the area and move on. I have the welting pieces about 6-8” apart. When you get back to the rear sail panel, skip over that and do the back window header the same way as the front. Pull each corner and secure it on the teeth and put a piece of welting there, the work back towards the center.
When all of that is done and the headliner looks smooth, it’s on to the sail panels, which are typically the hardest part to get wrinkle free. Work slowly and patiently towards the bottom, stretching from side to side. When all is said and done, remove the welting pieces and if there are small wrinkles, use a hair dryer on the heat setting and work them out. Elapsed time, probably about 2 hours.
Pics of my headliner, the spray adhesive I use, and the welting pieces I use, which came from an old Mustang door weatherstrip and push over the pin heels quite nicely.