A sunset, a sunrise, love, snow, a friend, a flower, a battle, a warrior, a king, a queen, a wolf, an eagle, something that articulates the mystery that currently puzzles you, a description of the scene around you, an honest, self-evaluative observation
Anything about love lost or love forbbiden is a great way to start
Love, death, tragedy...
Anything that you are interested in. Something that you know a lot about.
Well I don't know but I would say to like look on the internet for some of William Shakespeare's plays and maybe you will get an idea.