You don't. It appears to be a common misconception that you get double the annual returns. The fund tries to get double the daily returns, but also lags in this because of the high internal transaction costs.
I just started reading up on these leveraged funds. The leverage is not free, you will pay at least the risk free rate. Other costs include taxes on the dividends (much greater than a vanilla etf), high expense ratio, front end load fee.
Take a look at these articles:
http://seekingalpha.com/article/3119...struction-trap
http://seekingalpha.com/article/3578...leveraged-etfs