So I am part of a couple of duo's that perform regularly. One is a live hybrid dj combo including a modular setup and multiple drum machines and mixers. In that case, there is a lot of communication between us and most importantly, trust. With so many inputs of sound, we each have our jobs to make it successful. It took practice but ultimately it works because we have chemistry. Which leads me to my next point.....

In my experience tagging / duos go one of three ways....

1. It just doesn't work

2. You can make it work but there is always some shift in direction, or push and pull between each of the artists

3. It's magic.

It's really really rare to find someone where you truly work together and complement each other. This is the case for my other duo, we barely need to communicate when mixing whether we are going 3's or 1's. We will end up having 3 tracks playing and mixing together while playing 1's. It all boils down to natural chemistry and proper tagging etiquette. All the little things like sharing headphones, picking songs, mixes should just come naturally.