The MAF sensor is critical to power and fuel economy, but usually never gets cleaned, since it is upstream from fuel injection, and thus fuel system cleaners.
To clean it, remove the air box from the car, unclip the housing with the air filter, and unsnap the rubber air tube that leads from the MAF to the throttle body (there are some simple snaps on the side. The part that the wiring harness leads into is your MAF housing. Unbolt the two bolts holding it down, and you'll be able to see the sensor wires. DO NOT SCRUB THEM OR TOUCH THEM IN ANY WAY! They are fragile, and if you break one, you get to buy a new MAF ($200). Get some electronic parts cleaner (don't use carb cleaner or brake cleaner) and gently spray the wires until they are clean. Let the assembly air dry, and reassemble. There is a round mesh grille that you can either replace or leave out- it protects the MAF from debris in the air, but there shouldn't be any if you have an air filter. Leaving it out might get you an extra HP or two.
Some people think that running K&N air filters or any oiled cotton filter is bad for your MAF, since the oil mist from a fresh filter will make dust stick that would ordinarily burn off (the MAF wires are heated). K&N swears there's no problem, but it wouldn't hurt to clean your MAF sensor every so often, especially if you run a reusable air filter.
You should also clean the throttle body while you've got the air cleaner assembly off. Make sure the MAF is plugged in so the computer doesn't throw a CEL code, and start the engine. Spray bursts of carb cleaner into the throttle body, revving the engine with your other hand so it doesn't stall. Doing these little things will keep your performance and fuel economy as high as it can be, and might help when it comes time to pass emissions, too!