Decide on a design or stencil pattern you wish to paint onto your guitar.
Prime the parts of the guitar that need to be painted. Be sure that wherever you prime will be covered by your design, since it will not come off easily. If you want to completely cover your guitar with paint, you may wish to remove the strings and any other hardware that is in your way first.
Let the primer dry overnight.
Use the acrylic paint (and stencil if desired) to paint your design. Let the paint dry for at least four hours between coats, or between colors.
Give the guitar three coats of polyurethane, per the packaging instructions. Another option is to take the guitar to an auto body shop and let them clear coat if for you if you want extra durability. (Be sure to remove strings and hardware first)