Before you get started, measure your wall, or make a template of it.
Then prep your wall, sanding down any major bumps and making sure it is clean of any dust or debris.
You can print the dollhouse wallpaper on standard copy paper, but I recommend cardstock to avoid wrinkles from the adhesive and to even out any little imperfections you might have in your dollhouse walls.
Prepare your wallpaper sheets by planning your seams in advance. To join two sheets together, use clear tape on their backside. Draw the cut lines, and cut the exact piece you need very carefully.
To adhere the wallpaper to your dollhouse walls, you can use Elmer's glue stick, a liquid adhesive such as Mod Podge, or a spray adhesive. Use a credit card to smooth down the wallpaper until no bubbles show. If any paste oozes out, use a damp cloth to gently wipe it away.
Another option would be to use double-sided tape for a temporary version.