Between Instruments

1. The choice of instruments

If the instruments are paired in different categories, there should be a clear difference in timbre, so that the listener can quickly distinguish what is what in the music. For example, violin and erhu is a bad match. But a violin can be paired with a cello.

2. There should be a primary and a secondary

One instrument as the lead, another instrument as accompaniment, or in the main spin up and down around the action and sound programmed to proceed.

3. Don't always play the same notes

If you always play the same notes, the result may not be as strong as if you were playing a single instrument. To solve this problem, one instrument should play the melody and the other should play the harmony in 3rd or 4th. It would be a good idea to have someone who understands polyphony to come up with a counterpointed accompaniment.

Also: the matching of many instruments is a discipline called orchestration. It is content heavy and requires a foundation in harmony and polyphony. What I said above is only appropriate for two instruments, but only as a personal opinion. If you want to do chamber music, you'd better hire a professional composer to write the orchestration for you.