The most important point is to have an independent and proper administration. As long as there are corrupt governments, no matter how many resources a country has, they can't improve. Countries with economies dependent on external sources can't be independent in governance either.
Development is one of the most important factors for a country. If income distribution is not fair, even a country with vast resources can't become a developed nation. We know many large countries with oil and natural gas etc. whose people remain poor. We also know many small countries with no land for even agriculture that have become world leaders. In the end, it all comes down to solid governance.