Here are just a few of the things that I do to clean my city, with city meaning my local living area:

I recycle all paper, paperboard, cardboard, glass, aluminum, and plastic that I use. This includes junk mail and food packaging materials, which those two make up the bulk of my recyclables.
I grow plants in and around my living space. Not only do these convert carbon dioxide into oxygen they have " grown on me " become part of my daily routine and bring a smile to my face.
I drive a LEV, "Low Emission vehicle" and try to drive as smart as possible. This does not always happen because I have a bit of the lead foot syndrome but I try.
I choose water for 90% of my beverage intake. Creating a lot of benefits inside of my body.
I set up a recycling program at my day job, and now it literally keeps 5 to 8 tons of cardboard and paper a month out of the landfills, it has also saved the company waste disposal fees because it has freed up so much space from the dumpsters. Win Win situations are always good.