I once was asked to make a tutorial, how I wallpaper my houses. And without long opening speach, here's my approach:
I use: a set square, a measuring tape, a scissor, scrapbook-paper, double-faced adhesive tape and a pencil.
You see, that I took the pictures while I wallpapered Highfield farm :D.
Step 1: Take your house and choose a room to be wallpapered :D
I chose the childrens room in Highfield farm. Here it is without wallpaper...
Step 2: Measure the length and the height of one wall.
Step 3: Transfer the measurements onto the scrapbook paper and draw a rectangle.
Step 4: Now softly push the wallpaper at the wall, turn the house and trace the window shapes from the backside.
Step 6: Add the double-faced adhesive tape and stick the wallpaper to the wall :).
But what about oblique walls?
Highfield farm has two of them. I will show you the wallpapering in the grandparents room.
Like before, you have to measure the length of the room.
Then you measure the height from the middle of the wall to the top of the wall.
Now draw a rectangle - using the bottom length and the height of the top.
Divide the rectangle in the middle and draw a triangle, using the middle as the top.
Cut out and test, if the the wallpaper fits to the wall.
Use the same method as before to draw on the round window - add 5 mm, cut out and glue the wallpaper to the wall.
Edith seems to be pleased with the new walls ;)
I hope you enjoyed that little tutorial and I could help a bit. I'm not working professionell, but I always think, as long as it looks okay... :D
PS: I will make a post about my newest Christmas achievements soon :)