When the power goes out, a generator is only good if it can perform. That performance and efficiency depends on the size of the unit and how well it is maintained. A properly maintained generator will provide its power rating when running. A poorly maintained generator may only start the first time and then never run again.
Clean and Dry
The electricity produced by a generator is a godsend during a power outage, but it can be extremely hazardous when the generator itself is allowed to get wet and dirty. Conditions such as these create corrosion on the parts that conduct electricity. To prevent this, wipe down the generator after each use. Remove all built-up dirt and mud. Dry the generator by wiping it with a clean rag. Blow out ventilation cooling fins with compressed air, if available. Store the generator in a clean, dry and secure area. Inspect all electrical connections for signs of corrosion, which will appear as a white to greenish powder on the connections. Clean all corrosion and treat the connectors with an anti-corrosion inhibitor available from most hardware and home stores.
Oil and Filters
Change the oil and the accompanying filters as recommend by the manufacturer. Replace these components yearly, even if the generator has sat for a long period of time. Check the spark plug; clean the tip and gap. Keep extra oil, filters and spark plugs on hand. Test-run the generator at least twice a year to keep all internal parts lubricated and the fuel moving through the system. Add fuel stabilizer if the generator is only used for emergency backup power during outages. Gasoline will turn sour after a certain amount of time, typically six to nine months, if left untreated.
Inspect all bolts on the unit after the generator has cooled down from use. Vibration will loosen even the tightest of bolts over time. Keep a small tool kit that contains all the sockets or wrenches needed for servicing the unit. Include in the tool kit a screwdriver, pliers and a roll of electrical tape. Extension cords rated for the power of the generator should also be kept on hand. Inspect these electrical cords as part of a yearly maintenance routine, as rodents and other vermin may use the insulation as a chewing device.
Plan a scheduled maintenance twice a year; schedule the service time for predicted down times of the generator. Chances are the unit is only operated during winter and summer storms, so set dates for maintenance like the first day of spring and the first day of fall. Mark these times on the calendar as a reminder. Keep a record of the maintenance performed with the generator, too, so you can refer back to this record if a problem arises during operation. The goal of any equipment maintenance is to ensure the machine runs when it's needed.
Keep extra parts on hand for that 3am mishap where you brake something that you don’t have on hand and need for the generator to work and plan for needed items.
This Info found at eHow.com