You've been handed your assignment. You have a deadline. Now what?
Do NOT read any other reviews. They will poison your thoughts and put words in your mouth.
Commit time to read, listen, view, etc. The depth of thought involved in reviewing takes time and effort and should not be done last minute. It's best to have finished the work you're reviewing a full day or two before you start writing anything so that your brain has time to process and play with what you've taken in. This will also give you time to get over your immediate reaction and think past it.
While viewing or listening, focus on the important aspects that define the work. Write down thoughts or reactions and mark parts that you think are important to the whole. Take note of artistic devices like composition and lyrics in music, themes and perspective in cinema, voice and imagery in books, and technique and symbolism in art. Don't zoom in so close that it takes you an hour to read three pages of a book but don't run through an art gallery in 10 minutes either.
A good review is a balanced review. Anyone who says a work is perfect is a liar or hasn't been paying attention. There's highlights and failures in everything and it's your job to take note of both and critique them appropriately.
After mulling over the work for a day, get ready to write. Finding a starting place can be daunting, but a great place to start is to ask yourself, “Did I like it?” Then ask yourself why.
Next, there are two routes you can follow:
A. Free-write and get it all out so that you have something to work with.
B. Outline your review and fill it in. An example for a book review outline could be: I) This book is about..., II) Things that stood out or worked well, III) Things that didn't work, and IV) Overall review and recommendation.
Keep in mind that you're writing for an audience that has not yet seen or heard the work you're writing about and is looking to you for advice about it—entice with what's worth seeing or hearing and be honest about what doesn't work without giving spoilers.
Once you've written your first draft, reread it and edit it until you think it's done. (Hint: It's never done the first time around.) Then give it to your editor to review. That outside perspective is imperative because that is how everyone else who hasn't yet seen the movie or read the book will view your article.
Never forget the responsibility that comes with reviewing something. Respect other peoples' artwork and keep in mind that, as a cultural voice for society, you are advising the public about what movies, books, music, and art they should spend their time and money on.