Baby wipes are great for cleaning clear stamps....just be sure to get the ones that do not have alcohol as they dry out the stamps.
Try not to apply too much pressure and don't rock the stamp when using clear stamps so you don't distort the image. Stamping on an old mouse pad or proper stamping pad seems to help image come out better.
I often don't stamp directly on my layout/card because I'm afraid the image won't come out clean. I stamp on a piece of cardstock and fussy cut it out (cut close around an image) and glue it to my page. Also, if you use a stamping frame when stamping, the chance of being able to re-align your stamp to restamp an image if it didn't come out fully stamped is better.