I actually originally wrote songs to improve my guitar playing... And the focus on the singing and songwriting came a little bit later...

I noticed that looking up cover song tabs on the internet was either too easy, or the difficult songs, I had forgotten how to read sheet music... Guitar tablature helped but doesn't show timing or which finger should play the note or how to base it off shapes to make it as easy as possible...

... So I constructed my own riffs to challenge myself. Even with the songs I still play, I often have a simple structure but play little intricate riffs based on that structure inbetween the singing...

So that was my strategy to improve at the right rate... Almost creating my own riffs to stretch me and improve...