Take note of the lyrics. Try and remember a line or two from the song, and make sure that your lyric excerpt is something unique or different.
Search the Internet for the song title. Type the words from the song that you remember into your favorite search engine. Put them in quotes. If this doesn't work, try taking the quotes away. You may have misheard the lyrics.
Check Shazam. Activate the Shazam app on your phone and hold your phone up to hear the song. Shazam will then search its vast inventory of music and provide you with results in less than a minute.