Writing lyrics is the easy part in the creation of your song. Topics and themes are numerous and it is best to figure out first the theme before working on the words.
It is my believe that every good song should actually tell a story. What you must agree on first is the mood of the song. Happy, sad, funny. Is your song about love or lost love, dreams, hopes, fear, heartache and the list goes on.
Once you have decided on the mood and theme for your song then you must pick your music.
Defining the genre of your music is important. Is your song going to be rap, hiphop, country, rock?
If you want to create your own music to match your lyrics then several sites on the web can help.
These are the two that I would recommend as being excellent sources and so full with helpful info to get you up and running and find the magic beats to enhance your lyrics and get you to a top position on the charts.
Exmatriarch's Blog 