Welcome, O Padawan Metalheadi! Here's some advices -
1. Expose yourself to as much metal music as you can. You need to get it almost by osmosis. Most of us grew up listening to metal songs over and over, where we can naturally just 'feel' what is metal and what isn't.
2. Metal is typically about extremes. Experiment. Most of us did. Use too much gain. Go crazy on effects. See if you can scare your cat with your playing.
3. Communicate and congregate! Most metalheads have other metalhead friends. Musician metalhead friends are a bonus. We are real good about sharing the ideas and values of shit we enjoy, appreciate, and admire. In terms of both the music and the culture of metal. If you have someone you can jam with, bonus! We are big on teaching each other all the little tricks that make us happy. The heavy metal community is, despite appearances, usually a very gregarious, open, and friendly place.
4. Get a guitar hero. Learn how he or she did what they did. Become obsessed. I have many heroes, and they help inspire me to become both a better player and musician, as well as develop my own voice in terms of my approach to guitar.
1. Groove. Most metal grooves. Start practicing things that have a strong emphasis on the downbeat. Listen to drums, and maybe Youtube some metal drum beats to play along with. Accentuate those beats that tie in with the kick drum. Your picking hand is your friend.
2. Heavy. Some metal is fast, some is slow, but this isn't generally jazz we're playing. You want to be forceful in how you attack your playing, especially rhythms. Google search some videos about metal rhythm playing. Pay attention to how guys like Dimebag, or Zakk Wylde play. They really "got" the approach to metal. You can branch out from there, but this is the foundational stuff.
3. Sturm und drang. Most metal is pretty bleak and gloomy. It's generally why we liked it in the first place! It's dramatic, and we weren't always happy growing up. The anger and aggression of metal is a reflection of our youth. Typically metal is rooted in minor (as opposed to major) musical scales. Metal evolved from the blues, and the blues were sad. But it's not sadness for sadness's sake... it's a kind of way of celebrating still being around. A "fuck you!" to life's adversity. A decent understanding of minor chord/scale theory and pentatonics (5 notes per octave scale) is a good starting point. (Generally, AVOID MAJOR SCALES AND CHORDS! Until you know what you're doing.
4. Power chords. These are 2 or 3 note diads (the root and the fifth of a scale, generally, although I use a HELL of a lot of root/major-minor - the third scale element - diads in my playing.) Open low E string with the A string fretted at the second fret (the note B) is at the core of all of it. CHUG CHUG. Even experiment with downtuning. All of my guitars are 7 strings tuned down to low A.
5. Palm-muting. A technique whereby you rest the edge of your picking hand palm against the base of the strings where they sit in the bridge saddles. With a decent amount of distortion, this produces a heavy, percussive sound, that almost mimics the lowness of the bass and kick drum. It's a staple in heavy metal. Mostly used when doing metal rhythms on the lower strings. Best effect is generally using it mixed in with regular riff runs.
6. Can ya read tab? It helps. A nice guitar tab editor like Guitar Pro really helps learn what's going on in songs we're trying to learn. Learning how others did it is a key part of learning how we want to do it.
1. Distortion is your friend. Use it. You need a heavy sound to interact with so that you FEEL it inside when you play. Play around with gain levels. You typically want something tight, deep, and aggressive.
2. Typically with distortion comes the dreaded NOISE! Stop playing and your guitar howls!
We don't want that. A good noise gate (a device that cuts the nasty sound out except when you're playing) is a wise investment. A decent distortion pedal and noise gate pedal, or a small multi FX/modelling unit is a good starting point. Get one, and ask for some pointers on how to dial it in.
3. You already have a humbucker for your bridge. This is good, and true.
4. A badass amp doesn't matter a whole lot at this point. Can you hear yourself? Good enuff fer now. Bigger and badder will come later.
Something that allows you adjust EQ, that is loud and clear enough so that your tone is heard and produces what you hear in your head - ie., what inspires you, is fine.
There are PLENTY of exceptions to these rules, but you kind of have to really know and understand the rules first before you know what you're doing when you break 'em. I mean, this is why this isn't pop music. But this horseshit I spewed is what can get you on your metal path, and it's probably similar to how 90% or more of us started. Now watch this video and GO FORGE METAL!