Decide what kind of movie your poster will advertising. Your poster needs to successfully convey the emotional tone of the movie as a whole, as well as entice people to go see it. If you want to emphasize the movie's stars (either real or make-believe), then their images should be front and center. If there's some other aspect you want to emphasize--the epic scale or the special effects--then the poster should convey that instead.
Cut and paste various images to incorporate into the poster's design. Use pictures of various people or choose a single image for the poster. Composite images should be blended using software tools. Look for subtle distinctions in light and tone and iron these out with your software. Your image can fill the whole frame or just a part of it, leaving room for the tagline and credits.
Type up the names of the stars (along with a tagline, if you have one), and place them on the top of the poster frame. Leave a uniform space of 2 or 3 inches around the inside edges of the poster, where no text should go. Alternately, you can include (or make up) quotes from critics praising your movie, and place them at the top of the poster instead. Make sure the text color contrasts sharply with the space behind it, so it stands out better.
Place the title for your movie on the lower third of your poster. It should be prominent and in the center, without obscuring anything in the background. Leave enough space beneath the title to fit in the credits. Pay attention to the font type--it should match or come close to matching the font of the text in Step 3--and make sure the color you select for the title stands out from the graphics behind it.
Add a cast and credits list beneath your title, using the same font as in Step 3. The credits list typically lists, in order: the stars, the title of the film, any supporting actors, key crew members (production designer, costume designer, editor, film composer), producers, screenwriters and, finally, the director. Again, leave a uniform length of 2 to 3 inches around the poster edges, and make sure the text can be read clearly.
Include an MPAA rating in the lower left- or right-hand corner of your poster: G, PG, PG-13, R or NC-17 in America. If the poster is for a different country, adjust the rating accordingly.
Correct any errors or graphics issues before printing your poster out on a color printer.