Hi and welcome.
There are a few rockers here - check danieltrigger, but songwriting skill transcends genres imho.
Have a read of the rules and do a few reviews.
If you want to develop your lyrical capabilities then I'd select a title or theme and start to write something. Don't set yourself unneccassarty high bar. Perhaps follow a simple format like nursery rhyme for the verses
'Mary had a little lamb'
It's fleece as white as snow
And everywhere Shepard went
The lamb was sure to go'
Get a few verses down share it and ask for feedback. And once you've got a complete set of lyrics that you're ok with start on the music, post in wip and again ask for feedback.
There are techniques and 'rules' that can help, the more your practice the better you'll get, and interesting metal mayhem will surely result!
Neil