The compositor would not just “help any”, it would greatly change your scene. Adding a slight vignette(darkening the edges of the scene) would draw attention away from the edges and establish a focal area. If you color graded(tinted) your scene, you could establish more of a mood. And you could add glow and glare effects to the specular areas of the gun and the lit area of the phone.
To get started with compositing:
Keep in mind that Cycles doesn’t support renderlayers and some other things that, but there are workarounds to help simulate effects you can get in Blender Internal.