"Think globally, act locally" - or, how do you eat an elephant? Answer; one bite at a time. You pick something you can get your hands around and get to work. You do what you can when you can and don't second-guess yourself.

Not to speak solely in aphorisms, but Confucius said "If your plan is for a year, plant rice; if your plan is for a decade, plant trees; if your plan is for a century, educate children." So educate others about your activities when you can and lead by example the rest of the time.