The most common question I hear in the triathlete world about the mysteries of swimming efficiently usually involves something with breathing. In freestyle, the first step is to get your body position right. Then, you throw in breathing and everything goes haywire! This has to do with lack of balance, using your head instead of your core to breathe, and a few other factors.
To breathe, rotate your hips and think about breathing with your core or belly button rather than with your head. This will allow you to be more streamlined and balanced, as well as to be able to maintain your stroke rhythm.