Think like you're writing a symphony. By that I mean break out of the box of "2" instruments and try to think of multiple parts or sounds you want to represent the melodic line in the final mix.
Since both instruments have a large variety of sound, you can have one person doing something at the same time the other is doing something very different; the real sound willl be the final combination. If you think "melody first" and then work everything else to support that, you will find lots of opportunities to use simple, driving guitarwork to do the job. Less is more here.
So, for instance; if one instrument line is focusing on the lower register - the other can occupy a second or third chordal position to get some high tones. If one instrument is following a bass heavy rhythm, the other is free to explore the melody. If you swap lines, you can have one guitar running a rhythm line for eight measures, jump immediately to a lead melodic thing for eight measures and back again. The second instrument does the same in a reciprocal manner, so you have the melodic line being tossed from one to the other without missing a beat. EQ the instruments a little differently and suddenly you have lots of variety.
I'm trying to do that with multitracking, particularly with
Red Haired Boy on my Artist Launch site. Easier said than done...
One thing I'm doing is studying
River Suite for Two Guitars by John Carlini and Tony Rice. I simply can't think of a better tutorial for learning how to get what you're after than listening to that CD. It never stops amazing me, no matter how many times I listen to it.
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Red Haired Boy is at
www.artistlaunch.com/treeline