I think the bit about informal hierarchies deserves some expansion. It's worth keeping in mind they're often not even hierarchies, they're graphs/networks. The

I think the bit about informal hierarchies deserves some expansion. It's worth keeping in mind they're often not even hierarchies, they're graphs/networks. The most effective type of leadership is not by authority and forcing people to bend to your will; it's by prestige and people paying attention to what you do because they respect you, and you have a good track record of improving their productivity, be it with suggestions, mentoring, explicit training, choosing a direction, or something else. The directed, graph-like nature of these relationships mean that even as the most junior intern, you can usually find at least one other person who you help become more productive. And then you can slowly accrete more people you help be more productive, and eventually you'll find a large number of people agree you're a leader. That type of leadership is available to everyone, and it's a fast track to being more productive as an individual, through the transitive closure of the improvements you can drive with the help of others.