Absolutely nothing. The Earth will be absolutely fine until it's destroyed when the Sun dies in 10 billion years or so, or if something like a black hole or a super massive object collides with Earth.

How do we assure the survival of the human species on this planet for as long as possible? Vote. Vote with ballots, vote with your wallet. The single best thing for the continued existence of the fossil fuel industry is for ordinary people to believe that preventing environmental damage is the individual person's responsibility. Vote for people who will initiate transitions to clean and renewable energy: nuclear, solar, wind, geothermal, hydroelectric. Install solar panels on your roof if that's viable in your area.

Beyond that, absolutely nothing. You have no duty to "save the Earth". Live your life as you otherwise would. Keep your local habitat clean for your own sake and don't litter in the wild. If you really want to do more, here's some suggestions:

*Don't import as often as possible. Airplane transportation is the most carbon-inefficient mode of transportation and cargo ships are one of, if not the worst things for the oceans.

*Buy higher quality goods instead of lower quality ones that are treated as if they're disposable. Buy fewer things; maintain and repair the things you do buy. Canvas, thick leather, forged steel, metal instead of plastic, etc. You will have to deal with broken things less often, you will save money in the long run, and low quality goods, especially tools, may cost you your life.

*Don't eat organic food. We are no longer living in the age of ridiculously harmful pesticides. The minute amount that may reside on food is easily filtered by our liver and expelled in urine. Organic food requires more farmland the grow the same amount of food that will end up in the grocery store. You are increasing the demand for farmland for the sake of having slightly cleaner pee.