Rope in about a foot each way from the bottom center, then help seat that area of the gasket into the truck. Then rope out past each bottom corner about 8 inches and seat those areas (that will center the glass into the opening). Then work both sides up around the top corners, and seat those then do the rest of the top a half at a time. Be sure the gasket gets seated fully into the cab as the gasket will have a secondary lip that will hang up on the pinch weld.
I used this video as a reference:
https://youtu.be/zA8sX1KR6J0