So, starting off, this isn't an article into how to make ultra super br00tal whatever-metal, this should apply to all readers, although ultra super br00tal whatever-metal shall come later.
Dissonance is a blanket term used to describe bits in music that don't sound "right" musically (that's my perspective of it). The most well-known technique of dissonance is chromatics, which is the same scale for every instrument everywhere, and if you don't know what the chromatic scale is, start from any root note (that is to say, any note) and play:
R - sT - sT - sT - sT - sT - sT - sT - sT - sT - sT - sT
R = Root = Starting note
T = Tone = Whole step = 2 frets
sT = Semitone = Half step = 1 fret
Basically, pop music isn't great. I'm not trying to drag the entire genre down, or force an opinion onto anyone, but for the purpose of this article, pop music should be one of the furthest things from your mind, as diatonics are thrown out of the window.
Dissonance is often the key element to a song or certain type of music that makes them what they are. Dissonance can be achieved in many ways, from subtle changes in scales and modes, to full out chromatics and casual disregard for the listener's girly mentality. The most recognized pieces of music are the ones which really go deep into these realms and beyond, experimenting with structure as well as tonality, and this also explains why a hit from The Beatles will outlast a hit from Lady Gaga.
Some examples include:
"Bohemian Rhapsody" - Queen
"The Rite Of Spring" - Igor Stravinsky
"A Day In The Life" - The Beatles
"43% Burnt" - Dillinger Escape Plan
"For The Love Of God" - Steve Vai
We'll start with an easy thing first, which is one of my favorite modes ever, the Lydian mode. A basic rundown: Lydian is the 4th mode of the melodic minor scale, although due to its ascending pattern and tonality, feels like major/minor. Its commonly used in American media (TV and Film), a famous example being "The Simpsons" theme tune, and is also used by guitar virtuosos, most notably the aforementioned Steve Vai and also Joe Satriani. In fact, one the best examples of a nearly-purely Lydian song is "Flying In A Blue Dream " by Satch (back when he had hair)
The Lydian mode is played as follows:
R - T - T - T - sT - T - T - st
R = Root = Starting note
T = Tone = Whole step = 2 frets up
sT = Semitone = Half step = 1 fret up
The key note in play here is the 4th tone, which is the note that differentiates Lydian from your standard major scale (if you play C major and C Lydian one after the other, only one note changes). In a scale of C, it is a pesky little F#.
In tab (I use D standard, for E standard, just transpose the notes 2 frets down on your guitar), remember to alternate pick:
An example of the Lydian used to create both a major and minor feel is this song by Devin Townsend, excluding the pre-chorus (which isn't in Lydian or the diatonics, but does prove the usefulness of dissonance to highlight key points in a song):
One of my favourite tools for making or inspiring me to write with abstract dissonance is a scale called Super Locrian. Although almost strictly used in jazz guitar solo's (maybe for like a bar, or if the guitarist slips up, which is incredibly unlikely in jazz), super locrian highlights the use of dissonance in a scale pretty well, because when using only a few notes from the scale, it still contains enough notes to produce a melody of sorts when ordered in a certain way. The scale goes like so:
R - sT - T - sT - T - T - T - T
At first it just sounds really weird, and it is, it sounds even weirder than the whole tone, but dont worry, this is just an example scale that I'm suggesting to get you to experiment with dissonance. In tab, again in C:
And is even less ear friendly.
To highlight the extreme ends of dissonance, here are four songs. 2 use dissonances melodically, the other 2 use it as a rhythmical-cross-harmonic device (here comes the super ultra something something):
Tosin Abasi playing "Song Of Solomon"
Hiromi Uehara, featuring a song/solo
The Dillinger Escape Plan - "When Good Dogs Do Bad Things"
And if Death Metal isn't your thing, then try Stravinsky instead, and this peice should help you understand what bitonality is, as well as highlighting melodic passages over disharmony:
So, I hope this article has helped in some way, other than just throwing random things in your face/ears. The aim was just to bring awareness to the strengths of dissonance and what it can do to help you as a musician find your own way in music.