writing help

I have to write a story for school, the story is a continuation of the movie John Carter, i don't reallt have any ideas on what to write, so far Ive only written `"Ak Ohum Oktay Weez... Barsoom."

Finally after ten grueling years, he was back. He looked around and saw he was right outside Helium, he rushed in ecstatic by the thought of seeing Dejah again`

any ideas or tips on how to write better would be great