I always sketch the image I want with a grey lead first. You can erase pencil marks easily with an eraser.
I use acrylic paints...any brand I have lying around the house.
Try to use the smallest artist brush you can, especially when doing detailed pictures. Simply paint over your sketch.
Take your time. The stones will sometimes make your lines a little wonky..just take your time to smooth them out.
I do 2 coats. Make sure your first coat is dry first, then go over your design again for a strong colour finish.
Have patience....you need to let your stone dry completely before you add your sealant. If in a rush, use your hairdryer to dry your design.
I use Mod Podge as a sealant. This is available from most craft stores.
Don't worry when the Mod Podge goes on cloudy. As it dries, it will clear.
Two coats is best of Mod Podge. Wait for the first coat to dry before applying the second.
Enjoy your Story Stones!!!!