Micro-investing is a good option to consider if you want to keep building on your initial $500 investment. Micro-investing apps can collect your “spare change” and invest it automatically for you. For example, if you spend $21.25 at the grocery store, 75 cents will automatically be invested through your account. Those small amounts can add up over time, and before you know it, you may have socked away another $500 in your account.