Fuel undoubtedly the the very first thing in generator rentals. You should know what sort of fuel the machine takes. The rest gas, propane or diesel powered? You will need a safe, approved, portable diesel generator container to keep fuel. Plastic gas containers should possess a fire safety shield which prevents explosions by ignited fumes that enter the can. Furthermore, a good can will have a spill proof nozzle, special seals that reduce evaporation and vapor, child-proof design no secondary vent holes. Newer cans often times have all people improvements even better.
Never point it at someone or get too close about what you're cleaning (you can become hit by flying debris or water bouncing back off the surface). Ideally, wear safety glasses and close toed industrial diesel generator trainers. If using a noisy gas or diesel powered model, you'll need to wear proper hearing security.
First - here is the simple science of hydrogen fuel cells.