Run some kind of water pressure gauge
Use your motor often
Use E0 gasoline if available and if your motor will sit for any amount of time
Follow the break in period if new
Spray under the cowling with an anti-corrosion spray of your choice
Check the anodes. Not much should happen here, but occasionally they go missing
Check for fishing line wrapped around the prop shaft
The 2-stroke yammi 115 is a pretty good motor. As long as you keep the right mix of oil in it, or the oil tank full if it's got a metering system, it will run a long time. With that, just service the lower unit, fluids and impeller, each year or 100 hours, and change the spark plugs then too.
Also the suggestions above are good. Keep it clean and right and you can get decades out of that motor.