I suggest reading the reviews that the BellaOnline editors write. Go to a subject that interests you. Read reviews. Which did you like? Why did you like them?
One of the best ways to become a good writer is to read well-written articles. Then, write a short review of 400-500 words. Choose something that interests you to review. Ask a friend to give feedback on what you have written. Then, use the comments to rewrite the parts that needed work. Get more feedback, and change what needs to be changed. Do this until your article is just the way that you want it to be.
Writing is rewriting and rewriting, and rewriting until what you have written satisfies you. It takes time, work, and the ability to criticize your work, in order to improve your writing. There is no magic formula for a well-written review...only hard work.