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.

If you are powering a medical device, have a small back-up genset for at least that device.

Few additional thoughts off the top of my head...

If you're going to feed your whole panel (which I recommend if you have half a brain...) make sure to get a 240 volt panel so you can likely use everything you have (not at the same time). You might want to turn off circuits you don't need or can't run at a given time.

Consider a soft start for your air conditioners to make it so a smaller generator can start them. Many of these have to "learn" with grid power so install it before you need it and know soft starts can fail. Have a spare contactor and capacitor(s) on hand. (ask me how I know...)

Agreed, never back feed, never use a suicide plug. But if you're goign to do a portable generator consider a generator interlock (not legal in Canada) or a generlink. Both are usually cheaper / easier to install than a manual transfer switch or a generator sub panel.

While I agree portable open frame generators aren't meant to be run in the rain, and elevating them (for snow and flooding) and protecting them from rain / snow is advisable, I note that I see open frame generators mounted on trucks every day and I'm pretty sure the guys that use them work in the rain and snow. I have in fact run open frame generators in the mud / rain on constructions sites. Is it great? For sure not. Dangerous? Probably. But you have to weigh safety risks and risks to equipment yourself.

Finally, regarding fuel, in my opinion by far the best fuel is diesel. Safer, potentially very long lasting if well stored, and energy dense. If you have an oil furnace you can probably run your genset off of that oil.

If you're going gas / portable, consider a tri fuel, especially if you have natural gas at your primary use location. Duel fuel worth considering too. Even if you plan to use natural gas (why wouldn't you) or propane, have at least two portable five gallon cans on hand in case you have to rely on gasoline (or diesel above).

I love the NATO Jerry Cans but fuel cans are a personal choice and I trust you to pick what works for you.

I personally have 15-20 gallons of gas on hand at all times and I am prepared to ramp up to 80+ gallons if a storm is forecast. I treat it with a preservative that should keep it working for a year (with Pri-G I can retreat to make it last longer, in theory) then I burn it in cars every six months. The preservative is a safety net. In addition, a portable generator is my second form of backup power if my solar / battery system can't keep up.