I would recommend reading a lot of personal growth and development books. People think that they don't need it, but there is a lot of great content on there that talks about self improvement. I love reading a lot of John Maxwell books as well as Brene Brown books! I would also write out positive affirmations and repeat them every single day.
Reading or listening audiobooks. I would recommend you to look for this book: The compound effect by Darren Hardy. This book explain how little things done regularly and consistent could start helping you to improve your self. I also recommend that you make a self-observation to identify what is what you would like to improve, that way your efforts are focused and you can direct your energy on one thing. Other authors I'd recommend are Robin Sharma and Brené Brown. Have a successful journey.
Reading has been mentioned in the answers above, but I would recommend going beyond self-help literature and reading other material, too--such as philosophy, history, religion, and biographies. I have learned a great deal by seeing how and why other people made the decisions they have. A biography on Napoleon, for example, taught be about compartmentalizing aspects of my life so I could better focus on one thing at a time.
I believe that books are still the best way to expand your mind and to learn about the wider world. That will give you more wisdom and a better idea about how you can live a better life.
You can improve yourself as a person, by setting achievable small goals that ultimately lead to bigger attainable goals. These goals will push you and the success from completing the small goals will, encourage you to keep going towards the larger ones! It’s also important to surround yourself around the people who are the type of person you see yourself like. By going in the direction of them you develop like habits and a similar lifestyle. Your exposed to the things necessary to be the type of person that does the things you like and your habit will form thus giving you a better you. Be kind and do things out of love because putting out positive energy will radiate it back to you! Don’t forget to continue the things you like about yourself and love the things you do not like about yourself.
Give you an opportunity to know yourself, inner exploration is a good way to do that, there are very interesting books that you can read regarding meditation as well, is important that you accept yourself and identify your strengths, my reccomendation is you to focus on strengths instead of weak and develop them so that will help you to do things that maybe you never thought could be possible, it´s amazing.