In the general case, with some exceptions, we have found that two types of interventions stand above all others in terms of long term positive economic impact:
1. Infrastructure projects - like building roads
2. Gender projects - projects furthering women's rights in some way
These projects are long-term sticky and do not rely on continuous funding. A paved road will remain paved even after the funding is gone, and will have a positive impact on the community for many decades. Roads allow children to go to school in neighbouring villages, and people to sell their goods in a market, use a bike or other vehicle where they otherwise would not be able to.
Working with local governments to improving the attitudes towards girls and women often has a major impact on the economic output of a community both because more people can contribute, but also because the types of products and services become more diverse. This type of project is also sticky, once attitudes or structural barriers disappear they don't tend to come back.
Education or sanitation initiatives can be hit or miss, where, once funding dries up, all that is left is a non functioning latrine or empty school building.