Watercolor or Acyrlic Paint Setthese are the two easiest paints to use
Air Dry Clay Project
Water
Clear Coat or Varnish
Instructions
Dust of project before beginning.
Paint in thin layers.
Let each layer completely dry before painting on top. Make sure to not have too much water in your brush.
Once completely dry, add a clear coat to the project.
Notes
Let your air dry clay dry fully: This may be anywhere from 48-72 hours later. There are many factors that will effect dry time such as: project size, the thickness of walls, the brand of air dry clay being used and your environment.
Flat surfaces will work best when trying to paint intricate details. You can fix any issues with extra fine sandpaper first before painting.
Embrace the texture of the air dry clay and use your paint to enhance the natural textures already created.