hey, work with everyhting first to see whats good for you, don't sit down thinking i have to write something good just write what's in your head play with it, always humming, and strumming, but it works different for everyone
write to feel better, and to express yourself. pick something you feel strongly about, something thats on your mind and then make it universal, like when damien sings "too shy, i should have kissed you" everyone can relate but you know its personal at the same time. hope that helps, have fun with music, its beautiful