For the best stamped impressions, use a well inked stamp pad and make sure you place your paper on a smooth surface. For sharper images use coated paper (glossy or dull coated). You can buy sticky backed coated paper (from us or elsewhere) which can be cut and placed on any surface. For uniquely shaped stickers, cut with fancy paper edgers.
Occasionally, new stamps don't stamp evenly, especially the larger ones. Some people claim that it's some sort of residue on the rubber. My guess is that the rubber die is not seated perfectly against the cushion. In any case, ink and stamp a few times on waste paper, then clean as described below. You should see a marked improvement.
Sometimes small areas of a stamp (especially on large stamps), will not ink evenly. You can see this on the underside before pressing down on the paper. To improve the clarity, flip over your (raised) ink pad and dab the dry spot with a corner or edge of the pad and try again, but remember, it's still only rubber stamping, not offset printing.
I've found that ink pads tend to get used up (or dry out) much faster than most people expect. Rather than stamping harder to achieve better images, get a liquid re-inking bottle (called a re-inker) and use generously on your aging pads.
I clean my stamps regularly, especially when switching colors so as not to contaminate different pads. After removing dirt and hair with sticky tape, I prefer stamping first on a paper towel doused with a mild household spray cleaner, then onto a dry paper towel or napkin. You can also do the same thing with just wet paper towels, or you can use a stock stamp cleaner, which is a liquid detergent with a convenient sponge applicator on the spout. Remember, the thin rubber die is glued to the cushion backing, and the cushion is glued to the wood mounting block. Don't douse with water or cleaners because it may dissolve the glue and destroy your stamp.
The Sticker Dude