In practice we paired when doing difficult stuff. It worked well.
Don't pair at your desk. Use a pairing station.
Pair for a task, short if possible. If not, timebox.
Pair for short periods!
Train yourself to be productive while pairing. Don't relax. A short period of hard work.
Pick a consistent pairing time and make it a habit. Such as after standup, after lunch, whatever. Some times when you would not be productive solo, like after lunch, you can be productive in a pair. Experiment.
Long, unproductive, exhausting pairing periods. People will quit.
That one guy that nobody wants to pair with. Happens, sorry.
Sitting there twiddling your thumbs while your pair partner writes an email. Only pair for coding / debugging / testing! Don't pair at your desk.