Go forth unto a guitar tab site and scope a few Iommi riffs to play along with the record. From this all metal flows -- OK, that's an over simplification :) but however you tweak your amp, or however fast or slow you play it, that stuff is gonna sound pretty much like metal of one kind or another!
But, yeah, just keep playing whatever you feel like playing. In the end, your vibe, your arrangement, will be what ends up making music sound like what you want it to sound like. You could arrange and play Britney's "Oops" to sound pretty effin' metal if you wanted! :twisted: