68 dart headliner..

Worst mistake is marking the backside with a Sharpie or any ink pin.It will bleed through. Use chalk to mark general locations of dome lamp , sunvisors etc.. Hopefully you still have the original but it aint an absolute must have.
The little pocket like places where the bows end are 'V' shaped. This allows you to start at the back as stated before and pull the linner forward to 'umbrella' it up as you go forward.
If you'll get a piece of door edge guard and cut it into 2 inch pieces they will serve as handy little pins along the sides. It doesn't interfere with the trim either so you can just leave them there.
Even with the seats and stuff out of the car it aint easy. Dont forget to cover those floor hooks where rear seat bottom attaches. They will hurt you !
Good luck