Open and close seacocks regularly. Besides an annual disassembly and lubrication, constant use will keep them in shape and will alert you to problems before they become catastrophic.
Check your zinc anodes for corrosion. While you may have been in the same slip for years without problems, you never know when your marina’s wiring or your neighbor’s boat has developed an electrical problem. If they have, it’s your problem too. Stray current can eat up underwater metals quickly. So make this check a part of your regular routine.
Lube grease fittings and linkages. Spray engine, fuse blocks and ground buses with products, like Corrosion Block or Boeshield T-9, that dry to a waxy film. Spray lubes that stay wet attract grit, making more of a mess.
Writing down your impeller numbers, fuse sizes, bulb types, filter elements and other parts along with performed service like filter changes and pump rebuilds will prove a valuable reference over time.
Check filters visually, if you have a clear bowl, or by draining the contents into a clear glass jar. Like salad dressing, water and gas will layer, making water easy to see. Mark the date of service on the filter with a grease pencil for quick reference.