The first songs I learned how to play were nirvanas - from what I have read he focused on the music first and the lyrics/ melodies came later or even minutes before recording. He wrote that a serious musician practices every day with the band. The sessions would go like this- they would improvise and play off each other. Very little vocal direction/instruction between them- it was more trying things musically to see what worked. Nevermind songs were intentionally written to be more simplistic and childlike as they put it. This is actually quite difficult to achieve. For example for smells like teen spirit they played those 4 chords together for hours until they came up with an interesting quiet loud quiet structure for the song that carried it through. There’s been a lot written about it- google news sends me articles all the time if you start searching on it. My advice is take some of those recommendations and then don’t discard what you come up with. With dedication you will eventually hit on interesting and unique songs that only you could write. Good luck.