Look at it like a television script... when you change a thought within your scene, and have more to add use a comma. When you're done with an idea, and the camera would flip to contrast that idea, but still in the same scene, use a semi-colon. Then if you're going to a different scene on the same day...use a period A new stanza comes when you tell everyone to pack it up and go home. You'll pick it up where you left off tommorrow. Silly idea, but sometimes when I'm writing a poem thinking like that helps.