I would suggest that you just write as much as you can, sort of a brainstorming session. Pick a feeling, a concrete thing, a person or just a simple word, and write down whatever comes to mind when you think of it. Don't censor yourself when doing this, as it just kills your creativity. Don't worry about the quality of what you're writing, just focus on getting your thoughts scribbled down.
Do this often. I try to do it at least once a day, myself. It's great training when it comes to songwriting. Sometimes, when you read through what you've written, you may find verse lines or stanzas that you actually like, and you can then use them as a basis for a song.
Oh, and you should also check out this thread:
http://www.musicbanter.com/song-writ...ps-thread.html