Oneof the best methods for assuring straight, well glued edging in wallpaper application is the application of sizing first. In addition to making the wall slippery so the pre-moistened, pre-pasted paper can be moved around more easily.
One site also advises : "...Sizing also helps the wallpaper grip the wall better, and make it easier to peel off wallpaper later should you decide to remove it..." Sizing is applied like paint, using a paint roller and, at least here in the U.S. is fairly inexpensive. The sizing may even be allowed to dry before installation of the papaer...