grab a pick. thicker picks make your palm muting sound more crisp.
find a guitar somewhere and put it within your grasp
set up your amp for supreme distortion. most metal heads crank the low and high end, but I think that sounds like shit. use some mids you cowards. bump up your gain as well.
you gotta learn to palm mute. do this by putting your palm right where your strings meet your bridge. your hand actually goes on the strings to mute them and make them sound disgusting. see next step
here is a demonstration of non palm mute vs palm mute. this is probably the most important technique in playing metal.
start by playing a regular E power chord while palm muting. just strum a bunch of down strokes. (ps. I am tuned to c sharp here)
now try alternating between regular strumming and palm muting.
now try a more complicated picking pattern like triplets or something.
once you have all of that down. step it up a little more and try alternate picking where you palm mute one string and regular pluck another string. I am throwing in some hammer ons and shit.
you are now ready to join bolt thrower or slayer or something.