Accumulating Wealth to purchase an investment property

[Jacob D.]

I purchased my first home a little over a year ago in San Diego, CA. I am currently paying well over the mortgage but I have become increasingly interested in purchasing a second home as an investment property. My question/concern is what I should do with my money now to prepare/enable me to purchase a second home in the future. 

Should I continue to put more money into my current home than required, or should I do something else with this extra cash in order to allow it to accumulate and enable me to put money down on a second property? Any recommendations on investing this extra cash until I accumulate enough to put 20% down on a home?