For installing flooring and wallpaper, I generally use Duck indoor/outdoor carpet tape. It's very thin and sticky as all get out. I put a strip on the floor or wall then remove the protective covering and apply the covering. The protective cover is not always easy to remove so I sometimes use a straight pin to help separate it from the tape itself.
TIP: If you need to measure inside something (such as this back wall of the room), use two rulers the same size. In this case, I had two six inch rulers: the first, of course, was 6", the second was 3 1/4" so the total room height is 9 1/4".
Here I'm laying the floor in the sitting room. This is simple because this floor is wood and it's on cardboard. Put the tape along the sides and remove the protective backing:
Place another row of tape along the front and remove that backing. (You can also place a row across the back but since this floor is so solid, three strips work fine.
Align the flooring piece at the back of the room then drop it in place and rub down against the tape. Voila! Your floor is in place.
Same thing here with the bedroom floor.
Walls are a 'bit' more complicated but not too much. Cut your back piece of wallpaper to size PLUS 1/2" on either end. Fold a 1/2" piece forward on either end. Do the left hand side first then check for size and make sure the right hand fold is a good fit.
Put three pieces of carpet tape in place as shown. Remove the protective covering from the vertical piece and begin to remove the covering from the horizontal pieces.
Place the left hand side of the wallpaper in the corner making sure that it's even. Once that's in place, you can carefully remove the tape covering and smooth the wallpaper in place. When you get near the end of the wall, you add the final right hand vertical, remove that protective covering and smooth your paper in place.
Here I'm confirming that the left hand wallpaper fits.
There is a strip across the back at the corner...
Another strip of tape across the end of the wall
And that piece of wallpaper is in place.
Do the right hand wall and the room is finished! (Well, still needs baseboards but it's beginning to come together.)