The teenage years are an excellent time to study because the brain usually has a lot of energy for such things. So use this time well!
The easiest answer is to read a lot. If you haven't read them already, I recommend _The Study Qur'an_ edited by Seyyed Hossein Nasr and _The Scale of Wisdom: A Compendium of Shi'i Hadith_.
Beyond that, it depends on your preferred learning style and how deep you want to go. If you prefer listening, there are some excellent tafsir lectures online. (I am quite partial to those of Shaykh Mohammad Saeed Bahmanpour! But your choice, of course.) If you prefer reading, and are up for a challenge, you could always tackle the English translation of Tafsir al-Mizan. Quite a lot of it has been translated. If you do read it, I suggest getting a physical copy because it is easier to read than an e-book.
You could also see if there are any classes or discussion circles around you or online.
Sometimes just reciting the Qur'an and pondering its meanings unfolds meanings, and you could take that approach too.
Hope that helps! I am sure there will be other advice as well.