Need help writing song?

I am having an extrememly hard time writing a song. I kinda want to know what i want to write about. One is about religion and how i hate narrowminded ppl especially christans that say like im going to hell b/c i listen to metal. another topic is how like good music is dying bands like fob and mcr are the ones getting attention even though they suck. those are two ideas but idk how to go about writing them any help please. p.s. im going more for metal lyrics. i kinda want it to be half singing and half screaming.