I've written poetry since I was nine, and I would say I'm pretty good at it. I also really like music, and I can create simple melodies that I hum to myself. But whenever I try to write a song, my attempts fall flat, and I don't understand why. I'm good at rhyming and metering and I've written poetry before that, with a tune, could be turned into a song, but when I actually set out to write a song, not a poem, I am disappointed with the results. Is this common? And how do I fix this? How can I transition from poetry to song-writing, even though they are similar?
You have answers about the differences between poems and lyrics. I will focus on the how. What techniques can you use to make this transition?
I wrote a lot of song lyrics when I was in high school and the best advice I got was to write down lyrics of commercial songs I liked. I'm a lot older than you: there was no internet, there was no way to look up lyrics, and only about 1/3 of record album liner notes included lyrics (at least records were big so there was space to do it).
I'm going to give you the same advice but I'll warn you, don't just look up the lyrics on the internet then cut and paste. You need to feel the lyrics. Not just as part of a song, but the written words on the page. Listen to the song, pause, rewind, listen again. Write them down with a pen or pencil on paper. Or type them in to a computer. As long as you're feeling it where you write.
Figure out what the singer is saying and make guesses about how to break up lines and stanzas. Which part is the chorus (usually it's obvious, sometimes, not so much)? Write down the actual words, even if it's the same one 10 times.
When you're done, you can check it against a published source. Keeping in mind that a lot of lyrics on the internet are wrong. Or truncated. Also, if there's a difference between the official lyric and what the singer says, go with the latter.
Repeat the process for at least a dozen songs, preferably in the style you want to write in. In most cases, the words that move you deeply are simple and repetitive. You already know that's going to be the case. But you need to create it with your hands and feel it in your fingers.
Now start writing. Or take something you've already written and strip it down then build it up again.
What is central to your theme or message? Turn it into a chorus. You can change the words each time but they should be similar. Use the verses to tell a story. Or lay out a description. Or create a manifesto. Take a break after each verse to sing that chorus again, to let the words of the verse sink in.
Sing as you write. Or at least after your first draft. It doesn't matter if the melody is the one the song will go to. Make sure it's singable. The sound of the words is more important than the meaning.
Another technique is to write down ideas first, then sit down at the piano, guitar, or just on the couch, and sing it. Pull apart the words and use what works. You can start with a poem and sing that. Break it open and use lines, phrases, or single words that fit the song.
Does the poem (or unformed idea) have a story? Find the major touch points and make each one a verse. The chorus is the message or even the ending of the story. For example, if the poem is about the end of a relationship, the chorus might be about the breakup and the verses about meeting, the first sparks, deepening love, then the crisis you could not overcome. Your story can be about politics, friendship, the drudgery of schoolwork, or anything you want. Tell it simply and sing it loud.
Many of the most famous songwriters have either done just lyrics or just music. It's relatively common to excel only at one or the other. Personally, I write both but I tend to prefer only doing one or the other --I find it easier to write interesting songs with a collaborator. Since this is a writing forum, I'll focus in on the lyrics, but if you want to test yourself as a composer, a good way to start is to set a favorite poem to music, or to reset an existing set of lyrics with your own tune.
As a poet, keep in mind that most lyrics are poetic, but not all poetry makes for great lyrics. As compared to a regular poem, lyrics tend to be more repetitive, they are typically relatively brief, and they have a strong sense of rhythm, but their meter is not necessarily regular. If the rhythm is too unvarying it makes for a boring song. Great lyrics often seem to carry their own sense of melody with them, and syllables can be elongated or compressed in a way that would sound unnatural in an ordinary poem. They MUST sound good spoken aloud, not just when read silently. Lyrics also tend to follow certain structures, but I've written a lot about that elsewhere, so I'll just link those answers here. Most great songs tell a story of some sort, but the storytelling tends to be compressed, elliptical and cryptic as compared to other forms.
Great poets tend to make great lyricists, but it's not an automatic transition. Like any new form, it must be mastered. It's not unusual for new songwriters to write hundreds of songs before creating one that they like. Paul Simon spent three years writing every night before he created "Sounds of Silence," and Paul McCartney had the tune for "Yesterday" for years before he found the right lyric.
For your specific case, I would suggest starting with the thing you're least flexible at.
I've written poetry since I was nine, and I would say I'm pretty good at it.
I can create simple melodies that I hum to myself.
My guess is that you're able to mold a poem to fit a theme, but probably aren't so flexible musically as to mold a melody to be catchy, to match a specific emotion, and to incorporate a particular rhythm. So try starting with a catchy melody, and filling in an emotionally and rhythmically matching set of words.
You should also bear in mind that what makes a good poem is not exactly the same as what makes an engaging song. Songs, in my unprofessional observation, tend to be less dense than poetry that is intended to be read as poetry. That is, in poetry, there's usually more thinking, less straightforward narration, and fewer unclouded emotional appeals.
Compare Emily' Dickinson's (very good):
I felt a Funeral, in my Brain,
And Mourners to and fro
Kept treading - treading - till it seemed
That Sense was breaking through -
with Frederick Weatherly's
Oh Danny boy, the pipes, the pipes are calling
From glen to glen and down the mountain side
The summer's gone and all the roses dying
'Tis you, 'tis you must go and I must bide
Both are dripping with imagery, both are make at least light use of repetition, but they don't seem like quite the same animal. Maybe it's just that I haven't ever heard Dickinson (successfully) set to music, but while she is a great poet, most of her poems feel very talky to me. There really is a difference between good poetry and good lyrics, even if you're theoretically following mostly the same rules, and acting in many of the same dimensions.
At least one explicit difference I can think of; the word-choice in the lyric must bear the weight of the song's emphasis. That is, your long, drawn-out note better not fall on the "through" of the Dickinson piece, whereas "bide" would bear special emphasis.
(And, incidentally, "Danny Boy" was written for the tune, not the other way around.)