Margy and I pretty much adopt the John & Martha approach.
The person in the left seat is PIC and sets the rules.
The person in the right is free to make gentle suggestions.
Generally, Margy lets me play with the radios to keep out
of her hair.

In marginal VFR, whoever is left seat flies on instruments
while the right seat pilot scans for traffic. The right
seat and anybody in the back is on traffic lookout in
general. (The kids were quite bored with this job as we
usually spotted things before them until the time Margy's
son was flying with her to Oshkosh and entered the Ripon
transition).

We have the "run the tank dry drill down" Margy hits the
boost pump switch while I turn the fuel selector.

Of course there was the time I was sitting there all fat,
dumb, and happy in the right seat and we were coming in
to land and Margy who had been holding a bottle of water
up until that point decides to throw it in the back seat.
Except my seat is slightly farther back than hers and
suddenly I'm smacked in the head with a half-full water
bottle.

We won't go into the CRM required during 6 hour legs in
Australia.