I'm not sure if this will be of help since I don't listen to/write 80s-style hard rock/metal tunes. But generally speaking, I'll learn a couple songs from my favorite bands in the genre(s) I want to write a song in, and then experiment with different chords and keys until I get something original that I'm happy with. I've picked up on a handful of techniques that I've since started to employ more in my own songwriting from using this method the last few years, and it's really satisfying once your noodling starts to click and you belt out a more-or-less complete song out of nowhere.
YMMV of course, and you'll probably still wanna work on your material with other instruments and musicians to really round it out, but that's what's worked for me.