Depending on use, winches should be serviced once or twice per year, although some weekend sailors stretch it to once every two to three years. They are easy and quick to service yourself; they require few or no tools, and can usually be completed in about 20 minutes per winch once you get the hang of it.
While every model is slightly different, all modern winches are fundamentally the same. Check out this video for basic overview, and see the manual for your specific winch for directions on dissembling it.
3-in-one Multi-Purpose OilWinch manufacturers sell a "pawl oil" for 2-3 times this price. It is essentially machine oil, repackaged and marked up for a specific use.
Lubriplate No. 130-AA Multi-purpose greaseWhile manufacturers sell a special "winch grease", we prefer a calcium-based waterproof grease that has the same properties, is much cheaper, and can be used for other purposes.
Simple Green Cleaner and DegreaserA powerful and biodegradable degreaser will remove the old grease and dirt.
Replacement Pawl SpringsPawl springs often break over time or may get lost while servicing. Keep a set of replacement springs around just in case, and consider pro-actively replacing springs every few years.