Make sure you know about the subject matter. If you are writing a synopsis for a book report, read the whole book--if you are writing a synopsis for a film report, watch the film. If you don't know your subject matter from beginning to end, then you will not be able to summarize it.
Keep your synopsis short. A synopsis is a brief summary of your subject matter, not a long paraphrasing. Give yourself a realistic word limit to stick to. If you go over your word limit, go back and delete words.
Write the synopsis in chronological order. Order your synopsis in the same way as the narrative of the book or film: Start with the beginning and finish with the end.
Make sure your synopsis is equal in explaining the beginning, middle and end of your subject. An easy way to do this is to separate the book or film's story into three or four sections. Then shorten the sections to an equal amount of words, so that you don't weight one section over another.
Include the key themes of the book or film. If you are reporting on "Romeo and Juliet," for example, the synopsis must include the romantic themes of the book: the meeting of the couple, the difficulties they face and the outcome of their love for each other.
Reread your completed synopsis. Check for accuracy of spelling and grammar. Also check that you have not included any personal opinion on your subject matter. A synopsis is an objective account of the book or film you are reporting on.