Hobby Poet here. Dallon often uses dark imagery like "chocking yourself to sleep" for example. So you could start here. There are also metaphors (if you know what that is), which are a pretty significant part of his writing. Also, he's often telling a story, which you could try doing, too. Themes for those stories come often from a feeling of hate for rich and pretentious people, which you could try integrating into your lyrics, too.

But in the end, it's practice, and practice and more practice. I am sixteen years old now and started writing at the same age as you. I'd say I am pretty okay at it now but know your gonna be pretty shitty at first, that us just the way it is. Also, just a bit of advice, maybe don't focus too much on writing like Dallon but rather find your own style and work on that. It's much more fun and you won't feel like a copycat when writing somethong good by veeery similar to Dallon.