Think about the message. When you want to start writing a song, you must keep the goal or theme of the song in mind. If you do not have a theme for the song in mind, then coming up with one before you begin is highly recommended in order to keep you focused during production.
Inspire yourself. It is often hard to begin writing a song in an environment full of distractions. Taking time to separate yourself from others in a quiet place will liberate your thoughts. If you don't have a quiet place where you can go, then simply taking a mental retreat by putting on headphones and listening to some music will do. It especially helps if you already have the music for the song you will be writing.
Brainstorm ideas to overcome writer's block. Jot down your thoughts even if they are incomplete.
Take a short break by walking away from your work and doing some other activity to distract yourself. Return to your brainstormed ideas after your break and begin to expand on them little by little and you will soon have solid material.
Present the theme of your song in the first stanza. Entice the listener by threading the first verse of your song with echoes of its meaning enough to deny them from losing interest. Most listeners have to have their attention grabbed in the initial stanza so opening strong is essential.
Blend with the tempo and melody of the song's music. Most song writers start scripting a song to a melody and tempo. When you start writing your song, make sure that you understand where the music to your song will travel and try to match that feeling in words to the music. The music is often like a map to what the words of the song should be and details of the journey are filled in by the words and verses of the song. Ensuring that the verses are not too wordy for the music and that there are enough syllables to fill out the music, will make the start to writing a song easier.