First: how much poetry do you read? What do you like? Most writers find it helpful to be inspired by other masters of the craft.
Second: I see you are a 9th grader, which means this assignment is more than likely entirely creative. I cannot conceive of a 9th grade teacher who would scrutinize your raw ability as a poet. That said, my best advice is to block out a chunk of time for yourself, quiet things (no cell phone, computer, etc.) and just write what comes to your head. Freewrite, like you are writing in a journal. Try to write for 10 minutes without trying, just put down any thoughts that come to you. Then walk away from it for an hour or so. Feel free to do this exercise as many times as it takes. At some point, re-read what you have written and let an idea take shape.
As far as grading goes, I suppose as a teacher I'd remind you of a few things:
1. Poetry bends, but is not free from grammar rules. Spelling, punctuation, and usage all count. If you choose to bend a grammatical norm - you must have a reason for doing so.
2. Poetry does not have to rhyme.
3. Make it personal and enjoy it. Write without fear of judgement. Teachers can always tell when a student's heart is 'in it' or not.