How do I clean the drivechain?
Never go anywhere near your chain with the engine running.
There. You're warned.
All it takes is kerosene (look at Home Depot or the like), a spray can of O-ring chain lube, and a handful of old rags to clean your chain. Unlike gasoline, there are no explosive fumes with kerosene; it must be atomized or soaked into a wick before it will burn. Kerosene-soaked rags are a hazard; spread them out someplace (preferably outside) to dry before you toss them in the trash can. Kerosene is MUCH safer than gasoline.
WD-40 is not recommended for cleaning chains; it's not good for the O-rings. It may not be noticeable at each use but will add up. It's designed to penetrate and remove lubricant, and having permanent lubrication is what makes O-ring chains worth the money over standard chains, anyway.
Put the bike on the centerstand or rear stand and make sure it's in neutral, the engine is not running, and the pipes are cool to the touch.
Rotate the rear wheel by hand. Clean the exposed section of the chain as you go with your soaked rag. Try to avoid getting any cleaner on the rear disc or tire.
Once the chain has been soaked, keep rotating the rear wheel and wipe the chain down thoroughly and repeatedly with the old cotton rags, getting off all of the dirt that you can. You may use several clean rags in addition to the one with the cleaner on it. This is really messy, and you should plan on tossing the rags when you get done. Wear nitrile gloves unless you want to wash your hands for about an hour afterwards.
Try not to catch your thumb between the chain and the rear sprocket, as it really hurts! **#%!! Spinning the wheel so that the chain is moving away from the rear sprocket will prevent this from happening. And never go anywhere near your chain with the engine running.