First off, I wonder what you mean by your tears not being smooth. Any tearing with these will produce a worn, or distressed effect to the paper. You need to apply pressure when holding the guide in place while you use the other hand to slowly tear, gripping paper between thumb and pointer finger, closely along the edge of the guide.
It works very well with a thinner scrapbook or designer paper that is dry. For heavier cardstock I use the water pen tracing along the edge and giving it a few seconds to soak into the paper. It leaves a thicker, rougher edge to one side, and a smoother, but rough edge to the other.
I wish I could upload photos to show you. If you want, you can contact me at [email protected]
and I can send you the photos.