There comes a time in the life of every young axe slinger when he/she must venture out of the bedroom/garage/New York sewer and interact with other musicians, and maybe even — gasp! — other guitarists! And sooner or later, said guitarist might get bored with the sound of two guitars playing the exact same thing. It happens: often one player will have a different concept of the beat compared to the other, or one has a different attack than the other, and it just doesn't quite work when you both play the same thing. So what do to? Well you don’t necessarily have to arrange all your riffs like Def Leppard (Not that that’s a bad thing - an afternoon with headphones and a Def Leppard album can be a great lesson in writing for multiple-guitar formats) but there are many interesting things you can do to get the most out of a two-guitar band.
The best way to approach the lessons in this article is to grab a guitar and some kind of recording method, then lay down each track separately so you can hear them together, or so you can mute either one at will so you can jam along with yourself and explore your own variations. Treat it like a real jam with an actual second guitarist, and see where you can take it. But here's where to start:
Figure 1 is a simple 8th note strum on a Gm chord, played at 120bpm. Yawn. It's pretty simple, and not very ear-catching Figure 2 makes it slightly more interesting by delegating the bottom two notes to one guitar (which chugs them out with some palm muting), and the top three notes to the other. Play the second part more freely and maybe with some delay and reverb to add a nice sonorous chime. Personally I like to dial in a short reverb with a long pre-delay time, which almost gives the effect of a ghostly slapback delay.
In Figure 3, Guitar 1 picks out a few notes from the Gm chord while guitar 2 chugs out the same 8th note figure as before. If you have access to a few different guitars, try recording Guitar 1 with P90 pickups, and Guitar 2 with PAF-style humbuckers. This is a particularly good combination for these kinds of riffs, where you need a solid low end from the hum buckers along with a slightly rattier feel from the P90s.
Figure 4 is a further evolution of this idea, but more melodic, perhaps used as a main riff between chorus and verse in a vocal song, or even as part of the main theme in an instrumental. Really all you're doing here is playing a G Minor arpeggio over a sustained G Minor chord, but the interaction between the two different approaches to the chord helps to add a special kind of shimmer to your mix. You can emphasize this even more by playing a higher inversion of the chord either on Guitar 1 (the arpeggio) or Guitar 2 (the strum).
Figure 5 steps outside of the Gm framework a little. Guitar 2 (who seems to get all the easier parts in this lesson… poor Guitar 2) just strums whole-note G5 power chords while Guitar 1 gets all Queensrychean, playing a higher version of G5 in the first bar then dropping the fifth down for a deliciously evil tritone. The tritone is, of course, the most evil interval in music, but it's also useful in blues, jazz and avant garde music. Here it adds a slight sense of mystery and dread to the chord.
Finally, in Figure 6 we have something middle-period Metallica would be proud of, where Guitar 2 plays the same G5 power chord while Guitar 1 alternates between an open G string and fretted notes. Try playing a different chord for each of four bars in this style, and keep the rhythm of Guitar 1’s part but change the notes to match (or build upon) the new chords. Or just play four lots of this bar as-is along with a driving 8th-note baseline, AC/DC-style, for something a bit different.