While at Pivotal, I have worked on two distributed teams that involved remote pair programming.
Periodically check in about the audio, video, and screen sharing quality; fixes issues promptly
Setup a remote video feed when pairing locally
Leave the videofeed running
Leave the microphone open
Use a two display system. One screen is shared. The other is for supporting remote pairing
In an office situation, use a microphone splitter. When another co-workes interrupts you, ask them to join the conversation. Having a second headset makes this really easy. At the minimum, use a splitter to reduce friction. I use Scotch 35 Electrical Tape on black Belkin Speaker and Headphone Splitter
Use an expensive headset with a boom microphone
My personal favorite: Sennheiser PC 363D High Performance Surround Sound Gaming Headset
Avoid using earbud headsets as they tend to let in too much office noise. If these are more comfotable for you, check in with your pair about audio quality.