If you don't have a decorating bag, you can make one from a plastic bag or paper envelope. Spoon frosting into the corner of a resealable plastic bag and seal, or spoon frosting into the corner of an envelope and fold the end over. Snip off the corner of the bag or envelope to make a writing tip.
When using cookie cutters, keep a small portion of the flour on the side to dip them into between cuts. This will help prevent dough from sticking to the cutters.