The biggest factor that will change the look of your stamp is the paper being used. To test the imprint quality of your stamp, use it on plain printer paper.
Glossy, metallic, or coated papers: The ink sits on the surface of these papers and will take longer to dry. Too much pressure will make the ink smoosh out (very technical term) while you press down. For a cleaner imprint, apply less pressure.
Fibrous, textured or artisan paper: If the paper is looser weave, the ink will be able to bleed between the fibers. For a cleaner imprint, stamp a plain piece of paper a few times before stamping on your project paper. This will get some of the ink off the stamp and reduce the paper bleed.