unrequested advice:

Deconstruct songs.

Analyze how the masters [apply theory]

I put that in brackets because to me it's more like 

[how the masters compose harmonic structure]*

because cats like Cobain did it intuitively; 

but if you know some theory... what he does makes sense in theory terms

E.G.

"Breed"

To my ear it resolves to F#

so that's my tonal center/ 1

the intro/Verse Riff

Rapidly alternates between F#5 & open E (m7) + the sustained C# (5)

punctuated with the bend from A to Bb (3m, 3) classic blues move

then the open E (m7) to bring it back to F#5

makes a great riffing loop

Then the chorus

is just banging away on a diad of F#5 inverted and a higher register; so it sounds very different but feels like it belongs

then theres the thing of

so does it function like a Vsus4; because of the inversion; or is it functioning as a variation of the 1; becasue of the inversion, the F# is going to stand out more)..?

I'd think the latter; but to me there's some tension in it

but at the end of the day... it doesn't matter... because Cobain was just doing what he liked the sound of

then chorus descends quickly through dim5, 4 then open 6 then a slide from a diad of m3 and 6

the so whole chorus riff is really just riffing on the 1 chord; but it's got all this circular motion in doing so

the bridge 

m6, m3, dim5, 4; repeating until resolved with verse riff

*the same way visual masters use color and value and composition of shapes

or writers use aspects of plot structure and character and narrative; and etc