There are a number of ways we can clean up our air. The easiest way is to plant more trees, since they undergo photosynthesis and consume carbon dioxide from the atmosphere and generate oxygen. During this process, they remove carbon dioxide from the atmosphere and increase the concentration of oxygen in the atmosphere. Another significant contribution would be to minimize the consumption of fossil fuels, such as coal, petroleum products, etc. These fuels, on combustion, generate carbon dioxide, carbon monoxide, soot, particulate matter, etc. All of these are harmful to us, either directly or indirectly. Instead of fossil fuels, we can use renewable sources of energy, such as wind energy, solar energy, etc. Or, we can switch over to cleaner fuels, such as nuclear energy or more efficient combustion systems. We can also ensure that gaseous emissions from our vehicles and industries are properly cleaned (scrubbed to remove harmful gases and particulate matter) before they are emitted to the atmosphere.
Hope this helps.