How can I improve my chances at grad school?

I’m interested in a math or physics MSc program that’s geared towards liberal arts students. I don’t have a serious background in either, although I am a math minor. I will graduate with a GPA somewhere in the 3.3–3.6 range, I am confident that I will get a perfect or close-to-perfect GRE score, and I want to go to at least a fairly good school. It’s too late now for me to apply for next year, so I have time to take classes or whatever (I’m graduating next semester from a very good private college). So, what can I do to improve my chances?