You should have the door windlace installed so you can slip the headliner behind it. It helps hold it in place while you get it worked forward. Also the windshield trim should just be loosely in place as the headliner gets tucked above it. Ron's suggestion of attaching the center bow to the front section is essential.
I was actually surprised that I didn't have that much trouble with mine. I may be doing it again though as I had a windshield leak that softened the headliner at the front center and caused it to pull away from the windshield trim.
