Soft chocolates made of ganache, or chocolate covered fruit peels are the easiest to make from polymer clay. If you want to make a full box of any particular type, roll out a fine cylinder of clay in your chosen base color, and use a single sided razor blade or a polymer clay knife to cut even pieces of clay appropriate for the size of chocolate you are making.
To Make Chocolate Covered Peel - cut thin strips of clay and curl it into a gentle S bend using a glass headed pin or some other modelling tool. Pull up on the ends so that the strip is not perfectly flat to the surface.
To Make Chocolate Truffles - Roll small balls or short logs of polymer clay and press the surface with the head of a pin to create rough angled surfaces like those found on truffles. Bake the polymer clay chocolates and then coat them with an appropriate color of pastel to mimic dark cocoa, cinnamon, or pulverized sugar used on white truffles.
To Make Foil Covered Chocolates - Cut small bits of thin colored foil and use tweezers to bend the edges towards the underside of the foil. Keep turning the foil under with the tweezers until you can no longer see the edges, then crush the foil ball slightly into the shape you want (squares, circles or oblongs are the most common).
Sugar bon bons and Decorated Chocolates - roll basic chocolate shapes and decorate them with fine grains of colored sand to resemble colored sugar. If you have micro glitter you can sometimes use that to resemble the edible glitter used by some speciality chocolate shops.