[header] How to hang prepasted wallpaper [title] Buy a plumb bob and hang it from the ceiling. [step] Mark the vertical line in several areas on the wall. If your walls or windows appear crooked compared to these lines, consider a random wallpaper pattern so the edges and corners aren't noticeable. 
[title] Ensure there is enough room to view your pattern. [step] Generally, large prints don't work in small rooms because they make them feel smaller.