If you are interested in writing short sad poems than here are the right steps to do it: Think about a morbid topic and try to describe it with some metaphors while use wide vocabulary. In this way you can share your sad quotes while making them a universal topic, meaning by using metaphor, the subject of your poems will be obscure, but from the other hand it will capture the imagination of the reader who might understand something else from this art form - something that is much closer to him.