It is usually recommended that a generator be "exercised with load" on some schedule ranging from every month to every two or three months or as frequently as you can remember to do so. This is the best advice, and I recommend that my friends follow it.
However, years ago I realized that I'm not going to faithfully follow a regular schedule like that. I've got too many obligations for my nerve center to handle already. So, I have developed an alternative that has worked for me, as an outlier.
I have two generators in an insulated shed at home that back each other up. One is a 6000W diesel and the other a 4500W gasoline. Despite the best advice, I don't regularly exercise them between emergencies. This is what I do instead:
With my diesel genset, I keep the fuel tank and fuel system full at all times. It is my first-call alternative when the utility power fails. I don't worry much about the fuel going stale since diesel has a relatively long storage life and I don't use bio-diesel, which can go bad as fast as gasohol. My supply of diesel is kept in six 5-gallon tanks and replenished every couple of years or so. I cover the genset with a tarp, and in its frame I have placed a couple of 120VAC "Golden Rod" dehumidifiers. These are low-wattage electric heaters in the form of 18-inch-long tubes, placed at the bottom of the genset frame to keep the air a little warmer than ambient and circulating via convection. The theory is that this wards off moisture that might otherwise cause harmful corrosion on the genset. I live in a very humid climate.
With my gasoline genset, I drain the fuel tank, run the carb until empty, unscrew a drain screw in the carb bowl to let it drain dry, then store the unit under a tarp. Here again, I use two Golden Rod dehumidifiers under its frame. I keep my supply of gasoline on hand in six, 5-gallon tanks, replenished every year and treated with Sta-Bil.
Also, since both generators are electric-start equipped, I keep a full-size 12VDC battery on hand that is connectible to either generator. I charge it as needed so it is always ready for service.
So far, both gensets start and run when I need them.