Most craft today will use some form of single lever control. The separate throttle and gear controls are normally quite straightforward with only the odd pivot and/or cable to lubricate. (Speed wheels etc excepted).
Diesel stop controls using automotive type "choke" cables need the inner removing and lubricating every year. (When a 33C cable breaks, use it to make a superior stop cable).
SINGLE LEVER CONTROLS
URGENT TASK :-
For some reason, the majority of private boats I have worked on appeared to have ignored the control cables.
These cables are attached to the control mechanism by some form of soft (brass) metal nipple. These need lubricating (Moly Grease) once a year. If ignored the nipple will wear through and snap at an embarrassing moment.
Gain access to your single lever control cable nipples and LUBRICATE them - change them if worn.
Check the end fittings are secure. Check the outer cable clamps are secure.
NEVER KINK OR STRETCH CONTROL CABLES
NEVER, NEVER LEAVE THE DISCONNECTED END OF A CONTROL CABLE DANGLING IN THE BILGE - if you do water will enter it over the winter and seize it up.
GEARBOX DRIVE PLATES
Many gearboxes are driven by an "all metal" version of a vehicle clutch plate that is bolted to the flywheel. This is illustrated on the next page.
The purpose is to absorb torsional shocks caused by the engine power strokes, protect the engine from sudden gear engagement, and to allow for a very slight misalignment between flywheel and gearbox input shaft.
There is nothing an owner can do to check this member but if a "tinkling" sound starts coming from the flywheel housing suspect the springs are breaking up and seek expert help immediately - the failure is likely to be sudden and complete.
More modern plates use plastic or rubber drive members, so they are near silent when they first start to fail. They may clonk into gear a bit more than they used to but as they deteriorate gradually often drive failure is the first thing the owner notices.
I would advise that the drive plate be inspected every 8 to 10 years on a private boat.
Always have this unit checked if the gearbox has been removed for any reason.