An easy way to simulate movement is through the use of highlights and shadow. If you add a highlight to the top of his torso/shoulders you can animate that tilting towards and then away from the camera to create the illusion that his torso is also moving, though you will want to accompany it with arm movement as Darth recommends.
Here is an example of both methods applied to your animation:
1. Highlights applied to top of torso to simulate the character turning towards the camera when his arm is back and away when his arm is forward.
2. Added a neckline to the shirt to assist with the effect.
3. Brought the shoulders back when he lowers his arm and forward when he raises it.
4. Moved his head forward one pixel to break up the straight posture a bit.
Something else you should consider is bending his torso forward somewhat as people only walk rigidly when marching or something similar. Also, he looks like he's wearing clown shoes to be honest; I would shave off some pixels to make them at least proportionate with his legs. This will also likely improve the appearance of movement for his feet as the front of the shoe never quite makes contact with the ground.
I hope this helps!