People often say "We need to leave a better world for our children." This is only partially correct. We need to leave a better world for everyone on the planet after us! But we also need to do what we can, right now, to improve the world!
Spread kindness and understanding. Face down bigotry and hatred with compassion and truth. Recycle! Whatever you can do, do it! Even if your sole contribution is picking up an occasional piece of trash, that's still more than others do, so feel good about it! Don't be one who takes and never gives back, we are all living on the same world, and we all have an equal responsibility to take care of it, for ourselves, those we care about, and the rest of our fellow beings, be they human, animal, rodent, amphibian... you get the idea. :)
Use your resources consciously, taking only what you need, and make sure there's some left for the next person. Care for your personal environment, as well as the global one.
Remember: We only have one world. If we mess it up, where will we go? How will we live?