Huge numbers of people lack sufficient food, water, safety, and shelter. Others have these, most of the time, but lack the security to trust that they will continue to have them.
How can I help people? How can I most improve the world?
As a first world professional, a strong option seems to be "earning to give". I work to make money so I can give it to the most effective charities I can find. For me this means working for Google as a programmer and giving to GiveWell's top charities.
You can read more about this approach:
Update 2017-01-03: I'm going to be leaving Google, and while I'm still going to be donating I think the main impact of my work will now be direct work. (more details)