Well, I've seen a lot of columns on how to write lyrics, but not too many on what to write for lyrics.
This is also something that might help with writer's block. Sometimes nothing helps better to get rid of writer's block than a list of things to write about, even if you like only one of the ideas. Here's a list of things to write about.
Things you care about:
Write about the things/people/places/ideas or whatever is dear to you. For example, maybe your love in life (not necesarily a person, but also an activity, a place, a hobby, anything.)
I don't give a darn when/because/about, etc.:
If you can't think of something you care about, you can always write about something you don't care about. Something you don't like. Like a person you don't like, an activity you just don't get or care for, anything you don't enjoy. However, be careful that you draw the line between venting and complaining. To an extent, we don't want to hear it.
Metaphors about life:
Compare something to something. This is especially fun for the more experienced writers. Know anything that is similar to something in a strange way? Explain it. Here's one of my metaphors. ex)Emotion is fire.
Go take a risk:
Know anyone that has great potential but won't step out of their comfort zone, whether it be yourself, a friend, family member? Tell em to get out there!
Wonderment about a concept:
Everyone wonders about something. Here are some fundamental questions that bring up good song topics. Where will I go after I die? Where am I from? What is love? What's my/our purpose? Why do we suffer? How could they do that to me? Stuff like that.
A certain longing:
I know you want something. Saving up money for something? Any guy or girl in mind? Something you want to do? Want someone or something to be a certain way?
Take me as I am:
It's the title of a good Dream Theater song as well as a good writing topic. I believe one of the individual humans greatest desires is to be totally understood. Wouldn't be surprised if you want to be understood as well. Think life would be so much better if people understood you? Write about it.
Come as you are:
It's a Nirvana song as well as a good lyric topic. This is kind of the reverse of the previous topic. You want to be understood, you want to understand others. Essentially the topic's saying: Be yourself so I can understand you.
Now or never moment:
There are times in life where you meet decisions that change you drastically for better or for worse. If you have an experience like that, write it down.
A turning point in life:
I don't know if you are old enough to have a "turning point", but one thing to write about is something that changed your life, a change of heart, touched your heart for good. Either that or a point where you've started to go downhill, or slack.
Unity in something:
Are you a part of a group that believes the same thing as you, or does the same things as you? Talk about that. (By the way, it doesn't have to be a formal institution. It can be a highschool stereotype, your circle of friends, the people you associate with, the people you hang out with.)
Your idea of fun:
What do you like to do for fun? Hobbies? What brings you joy in life? What are your skills? What's your pride and joy? Tell us (as in the audience you're going to perform for).
On top of the world:
I know, it's the third time, but it's a Van Halen song as well as a topic. Any particularly joyful moments? Feel like you're on top of the world, like nothing is in your way? For example, from the movie "The Mask", "Somebody stop me!! Woohoo!!!" Yeah, that feeling. Pure euphoria.
Go away (insert whatever noun you like):
Want someone/something to just "be gone" because you hate them so much? Wanna threaten someone, "Stay away from me or I'll rip your head off like Ozzy did" Yeah... good for metal songs.
How long ______?:
Patience is a virtue. In the meantime, let's write a song about the wait. Are you waiting for something big to happen? Impatient? Really missing someone? Write about it while you're waiting.
Hold on to:
What do you hold on to? A person? A standard? What do you go by when times are hard? What's something to console you when bad things happen? Tell us.
If you've written anything else other than songs, this is a cool thing to try. Make a series of songs from a poem or story. It's also a good way to make quality songs quickly. I'm working on a concept album right now using a novela I wrote. It's so efficient that I can make a song out of each paragraph or two. (I'll be able to make a couple albums' worth if I'm lucky.) Also has a cool sound to it, all the songs in an album making a story. If you're curious, check out Coheed and Cambria.
Even after this, if you cant think of anything, you can write about how you can't think of anything to write. Just make sure that you make it sound poetic, and give it some thought. Otherwise it will sound stupid.
In memory of...:
Here's a good one. Are you missing someone or something that died? Remember, it can be about anything going away. It can be a dead person, dead genre, dead civilization, anything. Here's a unique example. I forget what the song is really called, but "California Rest in Peace" - Red Hot Chili Peppers. Good example of mourning something other than a person.
Just be careful with your word choices. Because the writing quality can make the difference between Helena - My Chemical Romance and You Raise Me Up - Josh Groban. No, I'm not bashing My Chemical Romance. I'm just comparing lyrical quality. And to you picky UGers, I picked Josh Groban to show the contrast of the lyrical quality and word choices.
Hope this helps! I found this thought provoking.