Education and Knowledge, Goal Setting, Communication, and Self Confidence.
These four things are essential in being a leader. You need to know the things to be a leader so that's where knowledge and education come into play. Goal setting is very important because you need to show the things you want/ can accomplish to be a leader. Communication is needed because you need to be able to talk to the people you are leading, you need to be able to hear what they have to say and you need to say what you want/need to say. Self confidence is also very important because you need to be confident to lead or no one will be confident in your leadership, people don't want you to not sound unsure because then they will most likely be like "oh lord he doesn't know what he's doing he shouldn't be making desicions."
President Roosevelt used all of these things in order to be the leader he was. He used his knowledge that he had and communicated to the people. He also made goals and effectively portrayed them to the people. He didn't faulter in his confidence so people followed him regardless if they were paying attention to the things he had to say or not.
I hope this helps!