The duets use the same selection of tunes as the Solo Arrangements. However, since there are a lot of things you can do with two guitars that you can't do with one I have made an effort to make the duets significantly more sophisticated than the corresponding solo arrangements. On a few I have stuck to tried-and-trusted approaches, for example on Turnaround where the accompaniment uses the 3rd and b7th of the dominant chords, and on Girl From Ipanima where the accompaniment uses the classic major 6-9 chords in the distinctive bossa nova rythm. In any case, I hope the techniques I have applied will stimulate your imagination and give you an idea about the many possibilities. When you listen to the examples, there are three things in particular I would like you to pay attention to.
The many ways to do accompaniment. The default method of playing chords and strumming is one approach but you should not limit yourself to that. There are a huge number of intereresting ways to support the main instrument, regardless of whether it is a vocal or another guitar. Always look for an original part when you are part of the backing, something you can claim you came up with specifically for that song.
Complementary parts are more interesting than similar parts.You have to find a way to add to whatever is already there. If the melody outlines the sound of a major chord, playing a major chord as accompaniment is not going to make much difference. You could focus the accompaniment on rythm instead of harmony but never blindly copy what you are hearing.
Timing is everything. It is like pairs in figure skating. Attention to detail is crucial. You don't want to go into the next manouvre earlier or later than your partner. The routine is beautiful when it is in perfect sync, and that is what you should strive for.
The duets are notated in tablature only. There is generally a lead part, M3-1, which carries the main theme and the melody, and an accompaniment, M3-2. It is occasionally necessary to use the fingers on the right hand to pluck several notes simultaneously. Keep the pick between your thumb and 1st finger, and use your 2nd, 3rd, and 4th finger to pluck the higher strings. You never have to let go of the pick, and in most cases you should be able to replace the right hand plucking with a brush of the pick if necessary.
Last but not least, playing a duet is fun! You get an element of interaction that is not there when you play a solo arrangement. So enjoy yourself when you are performing with your virtual partner!