Place bag in a bowl of hot water and let sit until chocolate is melted. Dry outside of bag and snip a small hole in one of the bag's corners. Squeeze bag over item to be decorated, making a thin line of chocolate. To make chocolate curls, soften a thick piece of block chocolate slightly in the microwave. Run vegetable peeler along edge of chocolate to make curls.
Transfer curls to wax paper and refrigerate until needed.
To help make melted chocolate easy to remove from a bowl, spray the bowl first with nonstick spray. Try to avoid storing chocolate in sunny or warm areas. It causes the cocoa butter to rise to the top and prevents chocolate from tempering properly when melted.