Repeat the same steps for each wallpaper strip, working from top to bottom. Once you’ve done the entire wall, take your box cutter along the molding at the top and cut a line in the crease all the way across, then do the same thing where the bottom of the wall meets the baseboards. It may not be perfect, (my hand slipped a few times!) but if someone is close enough to comment on it then they’re too close.
Windows and vents can be tricky. I did my best to cover them and then use my X-Acto Knife to cut out around the obstacles. Make sure yours is sharp or it won’t work well enough. Mine was pretty dull which is why my edges are kind of a mess up close! You can also use the scraps that are left over to go back in and clean up where you made mistakes. I wasn’t too worried about it because I knew my curtains would cover it for the most part.