Yeah, the best thing is to write the lyrics, and then figure out the music.
First you have to worry about your lyrics coming from the heart, your feelings or your life. the best time to write a song is when youre full some kind of emotion, sadness, happiness, anger.
Once you write your song and you feel satisfied, then start with the music. make your song interesting! not somethign that everyon'es heard before. start with a cool, catchy intro that will make the listeners interested in what you have to say.
Also when you're singing your song, sing in different notes, not just one dead line ------------------ experiment with different notes to sing in and keep it interesting. THE KEY WORD HERE IS INTERESTING =)
hope this helps!