I don't know if I can explain the proceedure well enough, but here goes.........
My car is a '40 Plymouth Business Coupe, I started by hanging the headliner by the bows, starting in the rear working towards the windshield. Once that was done, then I centered the material so that there was the same amount on each side of the car. Once that was done, my son was in the trunk to pull the material tight and we then cut a X shaped cut above the rear window at the interior light, then attached the interior light to hold the material tight, once that was done, we attached the rear window garnish moulding, again while my son is in the trunk holding the material tight. Once that was done we used hog rings to hold the material tight along the rear of the shelf. We then installed the rear side window garnish mouldings, from there we went to the windshield garnish moulding and installed that..
Using a plastic putty knife, we did the driver's side above the door, gently pushing the material between the windlace and serrated metal pieces that are above the door, that proceedure was repeated on the passenger side, then we cut the material out of the rear window and side windows, using single bladed razor blades. Aterwards we again used the plastic putty knife to push the threads under the garnish mouldings
We didn't use any moist spray or a hair dryer, but the wrincles aren't too bad and in the past week a good share of them have gone away.
Hope this helps, not professional by any means, but I am very pleased with the out come.
By the way, there was three of us that installed the headliner