If you're anything like me, you had piles and piles of great songwriting ideas laying around before you finished a single song. And a lot of songwriters I've worked with have the same problem.
Coming up with ideas is easy. But turning those ideas into complete songs is the hard part.
Stay focused on one (and only one) song.
Finishing your first song is a difficult hurdle to cross. But it's even harder when you keep switching directions, throwing away half-written songs, and starting over. So make it your mission to finish one song.
And take the pressure off: this song does not have to be your greatest masterpiece! This song is a stepping stone for you to become a better songwriter and for you to master the process of finishing your songs.
Keep your eye on the bigger picture.
Once you know what you're going to write your song about, outline the verses, choruses, and bridge and plan out what you're going to say (in plain English, no rhymes and no actual lyrics!)
Make sure you're constantly thinking of your song as a whole. When you're writing a verse, think about how that verse is going to fit into the entire song and how it's going to support the main theme of your song.
Then once you've written a part of your song, go back to your original outline and ask yourself, is this following the direction I originally intended? If it's not, you have two options: either re-work it to fit your outline better, or make changes to your original outline.
Keep it simple.
Look, I'm all about experimenting with complex chord progression, time signatures, cryptic lyrics, etc., but it's easy to go down a experimentation rabbit hole and lose sight of the direction you needed to go with your song.
Especially when you're new to songwriting, there's no need to go out of your way to make your song overly complex, unless it's 100% necessary to convey what you're trying to convey with the song. (And usually, it isn't!)
So I challenge you: Pick a song and get it finished. I promise, once you get past those first few songs, finishing your songs will get so much easier!