There is a really effective long shot art he beginning of a city or town with smoke coming out of it - we know there's trouble there.  Then the tanks start rolling in - this makes us think there is about to be a battle, which is what you expect from an action film.We then cut to a close up of a man with a beard, we know he will be important to the story.
In the opening scene of Expendables 2 they use a violin to create a setting of war.They do this by using a high frequency of the violin and they make it fast. As they start shooting they stop the violin and just have yelling and gun shots as the sound to make the mood of the setting war and determination to do anything to get what they need.
In Expendables 2 they use army wear for example a gun prof vest and a pair of trousers with lots of pockets to keep maps, spare bullets, communication devices and more to show that they are the heroes as they are prepared for war, for the bad guys they have dressed them up in everyday clothing like jeans and a shirt so they aren't prepared for a war.

The story line of Expendables 2 is that the good guys (you know if they are good cause they will have the most close ups) are tying to get one of their friends back from the bad guys (you will know that they are bad guys to the fact that they will look scruffy).

You know that it is a action film through all of the gun scenes and the fight scenes, you can also tell that its an action film through all of the war vehicles and excreta.