Wallpaper and Wallcoverings - Trimming Wallpaper

After I hang the wallpaper I have to trim it along the bottom and top and at the corners.

As I use an exacto knife I've been tearing the paper as I trim it, hence, it isn't looking pretty. I've put a straigtedge up firmly against the paper before using the knife (at least I thought it was firmly).

Is best to trim it while the paper is still wet or wait until it is dry, or when is the best time to trim and what tricks are involved.

I can pay someone to come do it, but it's only a small bathroom and I'm trying to do it myself.

Thanks for any help.

Ditch the Xacto knife pronto!! Believe it or not, they aren't sharp enough for the job. Buy a Olfa snap off blade type knife. www.olfa.com will show you what they look like. Don't buy a cheap knock off version or you will have the same tearing problems. It is preferred to trim the paper while its wet. Use a plastic spackling tool to use as a guide and "slide cut" along the top, bottom, and any edges. Use a fresh blade with every cut, no matter how small. I never trim more than the width of the paper without snapping a new blade. One trip to the wall for a cut, either the width of the paper or 2" means a new blade. Best of luck!