I have noticed that there are multiple guides that can help people to improve themselves as a lead guitarist. A rarer thing however, were guides about how people could improve themselves as a rhythm guitarist or songwriter although these are basic skills that, being a guitarist, you should be able to have. So here, I made a list of the things that helped me improve my playing style.
Improve your chords:
I know that most famous songs consist of four to eight basic chords such as G C F G and I know that you don't need a lot of (alternative) chords to write a good song. But, personally I think that, as a songwriter, you can distinguish yourself by using non-mainstream chord progressions. To me, if I write a song I try to challenge myself to put as much difficult chords as possible while it still sounds good. This is for me a kind of exercise to write more difficult songs so it keeps fun for me to play. Studying Jazz really helped me finding chords more interesting.
Improve your rhythm:
Every guitar player is useless unless he or she is tight on count. So before you start to use things like polyrhythm in your playing you should be able to play tight. Otherwise it just wont work. Practise with a metronome or drum samples. Let go the counting in your head thingy and learn to feel a straight 4/4, 3/4 and 6/8. Once you master this, you can start working with different time signatures or polyrhythm. But after all it is most important to play tight.
Study multiple styles of music:
By studying multiple styles of music you wider your horizon. Although you might not like al kinds of music such as Jazz or on the other side Hard-Rock or Metal, by studying and learning how to play these styles, you will discover unique techniques, chord progressions and dynamics which you can include in your own song writing and playing. For example, the first song I learned with a different kind of tuning was the song Slither by Velvet Revolver. The guitars were tuned in drop D (D, A, D, G, B, E). Now I use this tuning a lot in my song writing and not only for Rock. I also use it when I write a pop or folk song.
So all together, what helped me to improve my playing style and song writing was learning multiple chords and styles and learning to play tight. I hope that this also can help you.