Heres what i did to my buddy's 28 cig after it sat for 8yrs outside next to a wharehouse.
First find out how much gas your tank holds.....if full then try and drain some off. Water sits on the bottom so this will help pull any water that may be in the tank out. Top off with fresh 93 octane and then for good measure i added 10% Tolulene to the mix to help bump the octane of the old gas. I also added a bottle of heat just incase there was any water in there as well. And change the fuel/water filter.
Next i drained all the old oil out....This includes changine the outdrive and in our case the trans.....i didnt even start it cause i have been told oil helps keep moisture off metal so we didnt take any chances incase there was any moisture in the pan. Fill the engine with the chepest oil you can find and a new filter.
I pulled the distributor out and i have a priming tool i made from an old distributor and primed up the engine till we had good oil psi.
I checked the filter at the carb on this boat just to be sure there was nothing in there and we started the boat up......let it warm up...making sure theres no leaks etc.....then changed the engine oil to the good stuff.
Then we changed the spark plugs and tested the wires to make sure they were ok. Cap and rortor replaced...
In our case since the boat sat for so long the carbs needed to be rebuilt....so off they went. we also changed the belts and a few hose clamps that apparently werent stainless and were rusting. The impellers were changed and the old ones kept for spares as they actually looked ok!!!
That was 5yrs ago and the boat runs like a top to this day!
Good luck