If you've never said, "I need an anxiety pill, I have to wallpaper a dollhouse" you have either never wallpapered a dollhouse or you're one of those people who I envy who can just do it without any problem.  Me?  I have problems.

As for wallpapering... I went with the easiest possible method. Fabric with adhesive backing.  It has some give to it, and it's readjustable, perfect for imperfect perfectionists like me. 

Another great way to go is contact paper.  I find mine at the dollar store.  I look for patterns that are small enough to stay in the right scale in the house, or solid colors.  I'm not actually sure how well that's going to go on; it's a lot flimsier than the fabric, but I'll keep you posted.

The way I did it is that I measured it out, cut it along the grid at the back, leaving an extra half inch.  That extra half inch goes a little at the top, and a little at the bottom.  Who cares if the floor has a little extra schmutz on it?  It's going to be covered up by actual flooring later.  Similarly, if it's on the first two floors, the bit that's a little too tall is going to be covered up by the next floor up.  It's like, why bother making super fancy origami with your cheese if it's only going to be smushed into a sandwich anyway?  I feel the same way about the door and window frames.  I went over all of the cut seams with glue, after testing it on a sample area to see how it would discolor, and I'm probably going to brush glue all over the walls anyway, to be safe.
So basically blah blah blah wallpaper is hard.  But once you get it to look good, it kind of rocks. 

Here's Batman in my newly papered room in a chair that I found in the garage, chillaxing with a bear.

Happy arting!