You can't. It's random. Some players believe they can influence what GP they get by researching an associated tech just before getting the GP. The list is here: http://www.civfanatics.com/civrev/great_people. But I've never seen a 100% reliable method of producing the GP of choice. The most reliable ones I've seen are play as France and research only Masonry before your first GP. It is often a builder. Play as England and research Iron Working just before your first GP. It is often a leader. Pick any civ that doesn't start with a tech and research only Bronze working in the early game. Your GP will almost always be an explorer. But none of that is 100% reliable. It's possible to get a GP despite having no associated tech.