Pebbles, stones and rocks are great for painting on. You an look at it and eventually, or even sooner, a shape or theme will start to appear. The fastest one that I picked out recently reminded me of a boot, why on earth would I paint a boot you might ask? Well, there is that old nursery rhyme about an Old Woman who lived in a shoe, even though it says shoe it is always depicted as a boot so a boot it became, complete with door, roof garden, windows, laces and even a ladder leaning up against one of the windows so the children could use it as an escape route.
This particular pebble is tiny, only about 4 cm/1.3/4 in long and 2.5cm/ 1 inch high, if you would like to see more pictures of it they are available for sale in my Etsy shop, sad as I am to have to admit it, my own Kerioak site does not get as many visitors as Etsy does so I have more chance of someone loving it and wanting to give it a new home by listing it there.
I use very tiny brushes, Winsor and Newton acrylic paints and then seal with at least two, often more coats of acrylic varnish to protect it. I really enjoy pebble painting and they make great miniature works of art, you can see more on my Painted Pebbles page here on my site