I want to make positive impact to Nigeria. Show me how to be great. Where do I start?

Revolution and coup. That's the only way you can be remembered and make positive impact in Nigeria. My #2 opinion though

Greatness is a relative concept not a definitive one. Starting out to 'do something' and be 'great' can and often does happen especially in sports and music and very little else. As you may agree, milestones and achievements in sports and music are personal in nature and tend not to have a national hue. Now greatness can come from self-discovery. When you fully and completely understand yourself you would have transcended the need to be great. It is when you fully know yourself that you will be able to share the best of that self with the society and as such attain true greatness.