Gin:
This is my advice... after having taken a 2-day on-the-water with Capt. Mac.
1) Stick to the basics for operating the boat safely.
2) Docking bow in and stern in.
3) Things to set/observe before departing such as wearing life jackets, know where your emergency flares, first aid kit and safety equipment is, check fuel level, check engine oil level, check coolant level, check seacock valve position, electrical switches, thrusters power up, fenders, electronics powered up, VHF radio ON Chan 16, engine start procedure, throttle in neutral, raw water strainer bubbling, water exhausting from the exhaust port, horn working, cabin door open, helmsman's window open and so on.
3) Anchoring in shallow waters (if you have time)
4) Run the boat at various RPMs (weather permitting) and steer boat to port and starboard to get a feel for the boats maneuverability and stability at the various speeds.
5) Use trim tabs to adjust bow up, bow down, port side down/up and starboard side down/up... typically done at above 2500 RPM. This will give you a feeling for how to operate the trim tabs. Fuel burn can also be affected by the boat's trimming... but I wouldn't bother about this at first.
6) Note where switch positions need to be when docked with shore power ON and when underway.
7) Know how to activate the Inverter when on engine power only and away from shore power.
8) Do's and don'ts about waste tank pump out, re-fueling
9) What to do if underway and engine quits or sounds an emergency alarm such as over heating.
10) Basics for operating the VHF correctly, especially in emergency situations
11) Time permitting go over using Chart Plotter touch screen/menus and some basic Auto Pilot operations.
12) Manual operation of the bilge pump(s). Their breaker switches should be OFF as the pumps will power on when told to by the water floats. The manual switch is in case the float signaling fails.
13) Erecting/lowering the mast if you trailer the boat.
14) Have Capt. Mac help you setup the boat's configuration on the Chart Plotter such as draft, length and fuel on board.
15) Best practices for connecting the shore power cord, when to turn the dockside pedestal breaker ON and OFF.
16) If 1st Mate with you ensure they have a chance to operate the helm. Necessary if you become disabled or hurt in some debilitating way.
17) Check with Capt. Mac about what to watch out for if bad weather approaching.
18) Run the boat; a) into the oncoming waves, b) with waves following you... following seas, c) with waves/swells hitting your port or starboard sides, d) and so on per Capt. Mac's advice. This will give you a sense for how the boat reacts to such conditions.
19) How to check for Tides/current using your Chart Plotter
20) Paper chart policies
21) What are basic spares to have onboard ?
I'm sure others can chip in with what they consider 'the basics' to be, and my list above is certainly not definitive by any means.
[EDIT]
Suggest strongly that new boat owners attend their local USCG Boat Safety course... it really is interesting and beneficial to learn from the people that have tons of boating experience. It will also give you the opportunity to ask all your unanswered questions that mill around in your head. Take 1st Mate with you also.