I just did the headliner in my 69 myself, also my first ever. I think it might be possible to do with the glass still installed, but I can see that it'll be a lot harder to do that way for several reasons. You've got to clean the old contact adhesive off the "back" side of the metal strips that the headliner glues to, and with the glass in you're going to be working right up next to the glass, in the blind, into a space that's maybe a quarter inch wide. Likewise when you're ready to reinstall the headliner you'll have to get adhesive applied up into that area somehow, without getting it all over the glass.
There are some decent videos of the process out on youtube - just search for "headliner install" and you'll find them. Probably not specific for your model and year, but they're all very similar.
One tip that I got on here from Instg8er was to use binder clips (like for a stack of papers) to hold the headliner in place around the edges while you work on getting it smooth/flat and working out the wrinkles. When you get it "close" to right then you can work around the perimiter and glue it. That helped me a bunch.