First, locate it and make sure you have the proper tools to expose it. On one of my cars, I need a tamper-proof torx bit to access it. Once you gain access, you have a couple of options. The first one is to get an electronics cleaner spray and spray it down thoroughly to clean it, allowing it to dry fully before reinstalling. The second option is a Q-tip and rubbing alcohol. If you use this method, be VERY careful not to damage the mass air filament (usually a thin wire). If you snap the filament, you're in for a costly replacement.
While you have the air intake hose apart, now is a good time to spray throttle body cleaner into your throttle body.
Finally, it's a good idea to disconnect BOTH battery terminals during the whole procedure. This resets your car's computer to calculate the accurate air/fuel ratio (especially important if your mass air sensor was very dirty, as the computer slowly compensates air/fuel ratio for the dirty sensor; you want proper ratios for the newly-cleaned sensor).
Hope this helps!
