Prep the backing material if necessary. Clean and sand smooth. For a fresh or raw surface, prime with a high quality bonding primer.
Paint two coats of a high-quality Black Chalkboard Paint. A small foam roller usually provides the smoothest texture for the board. Allow to dry completely for at least overnight.
After the paint is dry, use white paint to add any decorative details that will be permanent.
For intricate patterns use a stencil and lay the stencil using painter's tape or transfer tape. Make sure stencil is completely flat and attached to the board so that paint won't get under the edges.
Season the chalkboard. take a bit of chalk and rub it all over the chalkboard lightly. Then use a soft cloth to wipe it off in circular motions. It may take a few times of doing this to get the real chalkboard effect.
Notes
I highly recommend a roller rather than a brush to keep the chalkboard paint texture to a minimum. Vinyl also has a great smooth texture and you don't have to wait for it to dry to use.