Website speed

I did a little testing on my website (mh-grafix.com) and the results were really good, except for one thing. Leverage browser cache was a score of 25 out of 100, is there anything I can do to increase this? I currently have the W3 Total Cache plugin enabled and configured. Is my configuration wrong? Is there something else I should be doing? Any help would be greatly appreciated.

Thank you.

mh-grafix.com