I am one of those SICs that trades off flying and non-flying duties. First flight is the Captains leg, next is mine, then capt's, then mine, and on and on. If it is an empty leg at the start or end of the day, and mine to fly, I'll do it from the left seat. I like to be comfortable in either seat. All the PICs have asked me, before our very first flight how I want to do it - left only, right only, or flip-flop, or whatever.
Back to the original question. In my limited experience, PIC does the exterior walk around. SIC is inside, cleaning tables, windows, floors, hand prints from the cabinets. SIC checks stock to see what is needed and stocks accordingly. If at a locker, either SIC or PIC if inside, gets stock and brings to locker. SIC makes sure ice, coffee, hot water, lav water, papers, and catering are good and on the plane. Once the back of the plane looks good, then you worry about clearance, ATIC, smashing buttons and checklists. Customers will and do show early. It has happened several times this week - 45 mins early. One person greets pax outside the plane and then takes care of bags, if there are any. The other greets the pax inside, checks manifest and IDs (could be done already), briefs on safety, catering, and flight time and conditions.
Then you fly. That is your job when the plane is moving. You do not have to tend to the pax. Most will not bother you. Some will talk to you if you are not busy, usually after we notice them looking at the cockpit and we speak to them. The majority know their way around the drawers.
One customer brought us some of his birthday cake, already sliced, so we would not refuse. It is good.
Another group of customers poured crushed pringles in the cubby hole where the phone is. Not cool.
After landing, one person goes out and gets the bags, the other says goodbye and then picks up the trash, wipes down the trays and windows, vacuums floor, orders lav, papers, and catering. PIC orders fuel, gets flight release, calls CANPASS if going to Canada (or puts out some other fire). Clean back, then checklists up front, repeat next flight.
The cleaning is easy if everyone helps out and you stay up on it.
Last flight is over and plane is clean, PIC does the books, SIC gathers the stuff off the plane, both put plane to bed (pitot and engine covers, batteries pulled, choked, brakes released, locked), figure out trans, go to hotel, call travel if reservations are messed up, order food for next day, sleep.
Sometimes you will do this routine only once a day, sometimes 6 times a day.