Read some DVD reviews from your favorite reviewers to get some pointers, but for the most part I'd make sure that you cover what you would want seen in a DVD review. I personally would include what acts are in each scene with the actors, but not give away plot information. Try to be as neutral as you would be with a toy review if you don't like something; it's ok to tell us that you don't like a specific actor or act, but don't make anything personal. For instance "I didn't like the amount of pubic hair this actor/actress has chosen to keep" is fine, but "This person is gross because they don't shave everything off" is definitely not ok.