Place several sheets of newspaper on the floor or on a sturdy work surface. Cover the work area thoroughly in case of spills.
Select a mold or form for a stepping stone shape. A simple round mold can be made from an inexpensive cake pan or a natural rock form available from a hardware or home store.
Place the form or mold on the newspaper and spray it with petroleum lubricant.
Add enough ready-mix concrete to fill the form half full. Pour the package's recommended amount of water into the concrete a little at a time and mix with a stir stick. Gradually add more ready-mix concrete and water until the mixture is just below the rim of the mold or form and is slightly thicker than cake batter.
Smooth the surface of the concrete with a trowel or, if desired, leave it rough to add interesting effect. Allow the concrete to set for 20 to 30 minutes.
Add decorative objects, such as pebbles, shells or colored rocks, to the concrete's surface. Press the stones, shells or other objects into the surface of the cement with your fingers. Alternately, you can use a stir stick to write or draw on the concrete.
Place the concrete stepping stone in a warm and dry location for 48 hours. Allow the concrete to thoroughly cure.
Remove the stone from the mold or form by inverting it onto a soft surface, such as grass.