Chocolate naturally has quite a bit of fat in its make-up. Because this is the case, it is not necessary to grease chocolate moulds when making candy, as you do with pans when baking cakes or cookies. The primary reasons that chocolate sticks to candy moulds are moisture, moulds that are not completely clean, or moulds that are too warm. Chocolate candies must be completely hard in order to cleanly pop out of their moulds.
Wash your candy moulds thoroughly at least a day in advance of when you plan to use them. Dry them with towels. Allow them to air dry overnight to make certain that there is no moisture or any foreign substances (such as remnants of past candy making) on their surfaces.
Pour your melted chocolate into the moulds as usual. Make sure to pour the chocolate only into the moulds, not on the plastic parts in between the moulds.
Refrigerate your chocolate moulds until the chocolate has completely hardened. Gently pop the chocolate free by pressing on the moulds from the other side. Handle the chocolate as little as possible to prevent melting it with the warmth of your hands.
If the weather is very hot and humid when you are making your chocolate candies, try to gauge the heat and humidity throughout the day. Days are generally cooler in the morning, so try to rearrange your schedule to work with chocolate when it is coolest. Otherwise, you may need to remelt your chocolate and try moulding it again if initial results are unsatisfactory. Covering your chocolate moulds when you put them in the refrigerator is not necessary, as long as you will be pulling them out as soon as they have hardened. However, if you need to leave the moulds refrigerated overnight or longer, cover them with a piece of cling film.
Do not freeze your chocolate moulds in hopes of the chocolate setting up faster. This can lead to chocolate discolouration (also called "bloom") or freezer burn.