Firstly I think no matter who you fly with its important to take command and act as a Captain. It is easy to fly with someone you consider to be better or more experienced and to wait for them to make decisions.
They make mistakes too. I remember doing a jet recurrent with an examiner who had 30000 hrs on every Boeing made. Apart from being the old type and bombastic he asked me to do a clean landing. Acting as my co-pilot he bugged my VREF at full flap speed. And then shouted because I was 30 kts high on his bugged VREF passing through 200 feet.
I smiled sweetly and commended him on trying to catch me out on VREF with the aircraft clean.
he almost choked on himself when he realised his mistake but I let him off the hook with a way out and earned myself no end of Brownie points
Shared flight in a single pilot aircraft is more a case of knowing who is doing what not who is captain and it is important to clear up with a pre flight briefing on what each pilots duties are. Ie " you operate the radios, select and confirm radio and nav frequencies with me. I will operate all the controls. I will operate the throttles, I will select flap, I will select gear etc. As Captain you must state every function you carry out to me and I will confirm.
On a multi crew aircraft so many functions including throttle, flaps and gear are carried out by the co-pilot, throttles are fine tuned on the takeoff roll etc. so much so that a strict format is used defining those duties.
In the relaxed atmosphere of a light aircraft with two pilot friends extra caution has to be taken regarding who is doing what as that is a recipe for something being missed.
Pace