Stephen Covey gives a useful framework: Do the intersection of your ability, the existing need, your interest, and the important. Ask yourself, "What can I do (ability) that other people value (need), that I like (interest) and that I feel is ultimately important?

Also, before you embark on saving the world, you might want to study a little Austrian economics. A lot of charity work and government programs are inefficient or actually contributing to poverty because they are contrary to economic law. You don't want spend few years of your life trying to solve poverty only to realize that you've been part of the problem.

In general, societies become wealthy when they are virtuous and economically free. Virtue causes them to generate and keep wealth. Economic freedom helps them build wealth efficiently. If you want to make any society richer from a macro level, you might focus on improving one or both of these: help that society become more virtuous and more free.

Regarding virtue, you might work to decrease drunkenness (Alcoholics Annonymous), drug use, and other vices. These activities harm individuals and their families and contribute to poverty.

Regarding freedom, you might work in politics to protect property rights, to have sound money and market prices, to allow people to work without licensing and other artificial restrictions, to reduce taxes. You can also work to spread price information and make markets more efficient (Craigslist, EBay and AirBnB do this.)

On a lower abstract level, you can work to produce some good or service which people value but is in short supply. That is, find a popular, over-priced good or service, and offer it at a lower price and better quality. Khan Academy is doing this for K-12 education.