More or less just common sense:
1. Clean your air/water intake screens/filters once a week if you are running your systems. This includes fridge intake and ac intakes (air and water). Lack of air/water flow will kill your equipment.
2. Keep batteries at or above 3/4.
3. Waterproof exterior canvas.
4. Turn water
pump/heater off when you are not on boat.
5. Check bilge for water and test bilge
pump regularly.
6. Clean waterline and prop regularly. While you are down there, check cutless and zincs.
7. Fresh water wash boat after each use.
8. Keep maintenance log and be diligent about changing filters, fluids etc.
9. Check oil every time before starting engine.
10. Know where all of your sea cocks are!!!!!
11. When plugging in shore power, turn power off at box while you are connecting.
12. Check every moving part regularly and keep them lubricated. Some parts need to be greased (sea cocks take water proof grease), some need to be oiled and some dry-lubed.
13. Check engine belts and hoses regularly. Listen to your engine - once you get to know its purr, you will notice the difference when something is going out.
14. Keep your engine clean. This makes it easier to keep visual watch on what's going on with it.
That's all the comes to mind at the moment. Feel free to add to the list...