Watch the movie two times
The first step to writing a review is to watch the movie in a relaxed, known and comfortable environment. This will allow you to concentrate on the fine details which are so important in a comprehensive review. Watching the movie a second time will make it better. There are some people who write the reviews after reading a lot of other available on the internet or newspapers. The practice is downright immoral and not recommended.
Give unbiased opinion
There is a good chance that a reviewer might personally like an actor or actress in a movie, and would be bent to dislike his/her performance. However, it is a moral duty of the writer to give a fair and impartial description of the movie and the performance of different characters in it.
Develop a taste for all genres
A good movie reviewer would cater for all genres of movies. Sure, personality counts a lot in writing, but a good movie description only comes when the writing is done by heart. And for that, a taste for every genre has to be developed.
Know your audience
Writing a full fledge review exploring the cinematography, photography, lighting and other technical aspects for an audience that is least interested is nothing less than a disaster. Before going for a review, a writer should know the nature of the people who will read his stuff.
Under no circumstances should a review make the error of revealing the plot. This is a cardinal sin, and can pretty much compel most of the people to avoid the suspense. This will not only reduce the readership, but will also cause great harm to the business that a movie does on the box office.
Support your criticism
It is a writer’s job to criticize the angles in a movie that he doesn’t deem good, but it should be done so with a solid argument.