Get a shop manual!
Ok, that said, the twine trick is pretty simple. Press the rubber gasket on the edge of the windshield (make sure it's right-side up). Wrap a single strand of twine around the perimeter of the windshield gasket so it fits into the deep groove for the cab lip and overlaps at the top by about 8". Then lube it with liquid soap (etc) and press it to the opening. With a buddy applying even pressure, you get inside and pull the twine toward the
center of the windshield (waxed twine slides better). This pulls the rubber inside the cab lip without tearing it.
All this is described and illustrated in the shop manual.
edit: I found the same trick worked very well for my rear windows in the panel "barn doors." I had to cut the gasket to length, so I used wood clamps to hold it to the shape of the glass and joined the ends with rubber cement. The next day I took it out of the clamps and did the twine trick. Just remember that when you're pulling the twine it should always cross the centerpoint of the glass.
