Watch the film two or three times, each time reflecting on its meaning and looking for anything that you may want to discuss at length. Take notes that include theme, mood, symbolism, photography, plot and anything that lends texture to the film. Write out bits of dialog that stand out as significant. Be careful to do so accurately, and use quotation marks.
Develop an idea for a thesis, which for film analysis may be as simple as recommending the film or not recommending it. Choose a thesis that you know you can defend with explanation, examples and logic. Keep the focus narrow: You don't have to write about every aspect of the film. For a movie analysis, place the thesis in the first paragraph, or save it for the last paragraph.
Set valid criteria by which you will evaluate the film. Theme, plot, characterization, and the use of lighting are all examples of valid criteria. Compare apples to apples. Arguing that the film fails because it's a western and you prefer modern crime dramas is not valid. Instead, consider the viewer's expectations of theme, genre, a lead actor or the director.
Include a short paragraph, either as the opening paragraph or the second paragraph, that mentions basic background, such as who the director is, who the key actors are, when the film was made, whether it's based on a book -- or other contextual information that may be of value to the reader.
Alternatively, include all the same information, but weave it into the rest of your essay, mentioning it as necessary.
Include a paragraph summarizing the film. Often the summary is in the second or third paragraph. Give the reader some basic exposition, including who, what, when and where. Mention main characters, plot points that are relevant to the rest of your discussion and theme. Mention whether the plot is engaging and believable, or cliched and silly.
Develop the paper, devoting one or more paragraphs to each main point that you want to make, and support what you say with specific examples from the film, especially those that relate to your thesis.
Avoid spoilers, if you are writing an analysis that will appear in public. Readers do not want you to give away the ending. However, if you're writing a scholarly analysis that only your instructor will see, it may be appropriate to reveal the ending -- if doing so is pertinent to your thesis.
Proofread your paper on hard copy, as well as on the screen. You will catch more errors and get a better feel for whether it works as a whole.