There are various things you can do. The eraser is one, and you can also wipe them on demin (your jeans will be fine) as these two things clean off any oils present from the manufacturing process. Another thing you can try is a Snow Block which is a very fine sandpaper block. This will roughen up the surface of your stamp just enough for the ink to stay and not bead. You will also find that the more detailed the stamp the better the print as solid stamps have a greater surface to collect the ink into beads. Also using pigment ink rather than dye ink should give a better print.
Hope this helps!
To live a creative life, we must lose our fear of being wrong. Joseph Chilton Pearce