I like studying the structure of Beatles songs, they seem to be such a good standard, but it’s subjective. Study the way the song is arranged and the parts and recreate the format and you’ll start to feel more structured and more adventurous to branch off and make it your own.

If I have a genre in mind, I’ll absorb that style for a bit and experiment with it after listening to some artists I like or discover along the way. And then just practicing a lot makes it all more familiar

Why do you want to improve your songwriting?

If your motivation is commercial success, look at past successes. There is no shortage of song breakdowns on YouTube. Improve your theory knowledge if you’re lacking in that department. Cooperate with other producers/musicians if you can. I fear there will not be much space for commercial success in this field in the foreseeable future thanks to two dreadful letters though.

If you are more of a hobbyist (and I would count myself among those), I just do the Carnegie Hall approach of practice, practice, practice. Trial and error. I can tell my music and production have much improved from when I started dabbling in this a decade ago. But I also still don’t think it’s good enough to release it.

Are there any consistent flaws with the songs I write, or just anything I could improve on in general?

Chiptune is hard to critique because of the self-imposed limitations.

Your best bet is to use reference tracks. Pick a song you like by an established artist that sounds similar to what you want to make, drag it into your DAW, and compare your decisions against that song each step of the way. Music production is a bunch of different skills that can be practiced and improved, and a reference track can give you a clear goal for each of them.