Help From Others Is Great But It Boils Down to You To Improve As A Leader
It's appropriate that we begin this section on self-development of leadership skills and abilities by starting with the issue of responsibility. Who is responsible for your development as a leader?
Since leadership entails taking responsibility for one's actions, it makes sense to embrace the "responsibility ethic" even before you have formal leadership responsibilities.
Apart from that, leadership effectiveness, once you are leading, rests on your shoulders, you benefit from achieving a leadership position, and you are probably in the best position to take responsibility for your own self-development, even though you may enlist help and advice from others about the best ways to develop yourself.
So, while your organization may provide resources (e.g. leadership training seminars, books, opportunities to develop your career), and individuals (e.g. your boss), can mentor and guide, it's still up to you to be proactive about going after these opportunities.
If you aren't willing to do that, and shoulder that responsibility, it may be that you aren't suited for formal leadership positions. There's no shame in that. You may choose to lead quietly without formal authority, or simply to focus on doing your particular non-leadership job. Not a problem.