Here are some things I've learned owning generators and running generators that do and do not belong to me. Improvements and additions are more than welcome.

Before you buy a generator:

• Understand the wattage of the things you want to power with your generator
• Understand starting watts (often called surge watts) versus running watts for your generator, and don't plan on using more than the running watts for more than brief periods
• Understand starting versus running watts for the things you want to power -- things like power tools, pumps, air conditioners, fridges, and freezers use up to three times their normal watts during startup
• Figure out a good place to operate the generator, outdoors, away from flammable materials, and away from windows that might open, and hopefully out of the rain
• Decide if you're going to use a transfer switch to power your whole house, parts of your house, or if you're going to use extension cords to power specific devices
• Invest in high-quality extension cords if you'll use them with a generator, and no longer than they need to be

After you buy a generator:

• Never, under any circumstances, backflow power into your house without a transfer switch -- this can be deadly
• Never, under any circumstances, operate a generator indoors, near a window that might open, or anywhere other than outside in fresh air -- this can be deadly
• Don't operate a generator anyplace near flammable materials
• Have a plan to operate your generator in the rain without it getting wet, if it isn't designed for that; I use a sheet of plywood but almost anything will do as long as airflow isn't badly impeded
• Ground your generator if you're doing anything other powering specific devices with extension cords (and it isn't a bad idea to ground it anyway)
• Read the manual that came with your generator
• An aftermarket magnetic dipstick can help you see and remove metal particulates in the oil, which can significantly lengthen the life of the engine
• Break in your generator as described in the manual -- but don't hesitate to change the oil more often than suggested -- my Champion generator manual states to break it in at no more than 75% load and change the oil at 30 hours, but the condition of the oil resulted in my changing the oil at 5 hours and again at 15 hours during break-in
• Always use stabilized fuel
• Have tools, oil and spare parts on hand -- I've obtained duplicates of certain tools to keep in the generator-specific toolbox

I'll post about the tools and parts I keep around later on.

And one more time: NEVER backflow power from a generator into your house wiring without a transfer switch! Do not ever even possess a "suicide" cord -- they're named that for a reason.