A foolproof method is to learn it by ear. It takes a while, but it is worth it. I grew up in a small Wyoming town where the closest music store was 120 miles away. I learned lots of songs off records and the radio. It was the best thing I could have done to train my ears, but I didn't know it at the time.
Even if you need the sheet music just for the chord changes, the above advice is still useful information methinks.