Here's how to get a professional look when you hanging wallpaper. After you line up your pattern, overlap the top and the bottom by about two inches. You should always cut each piece a little long. Then after smoothing out the bubbles and checking to make sure the wallpaper is plumb, use a five-inch putty knife as a guide for a perfect razor cut on the top and at the bottom. This will ensure a clean and crisp professional edge.
For more on wallpaper, consider:
How To: Wallpaper a Corner
12 "Off the Wall" Ways to Repurpose Wallpaper