Rules of thumb
I just happened upon Roger Ebert's movie glossary. It's a reasonably funny list of film cliches which he appears to have put together at some point in the middle of the 1980s. I thought these were some of the better entries. Check out the rest.
Any plot containing problems which would be solved instantly if all of the characters were not idiots.
Any character whose wife and/or kids are introduced more than an hour into the movie and who hugs and kisses any or all of them will be dead within the next 20 minutes. e.g., "Goose" in TOP GUN.
Invisible appendage used by Rambo in RAMBO, in the scene where he hides from the enemy by completely plastering himself inside a mud bank. Since it is impossible to cover yourself with mud without at least one hand free to do the job, Rambo must have had a third, invisible, hand. This explains a lot about the movie.