What's the best way to learn something effectively?
Rajesh Pathak
Every person follows his/her own learning style.

I find it easy when I take notes. Why? Because my school teachers used to ask us to take down notes in the class which they used to dictate during the class. Thus, I developed this habit.
Some people use highlighters to mark important sections in the book instead of writing down.
You must find out which method helps you. May be there are other methods lying around that your friends/relatives/parents/elders can share with you.

Also, you need to develop interest in the subject that you want to learn. Interest develops when the subject itself is of our interest or we know that learning a particular subject will help us to do well in our lives in future.

Keep revising what you learnt yesterday before taking the subject to the next level next day. Keep practicing. Once you know the entire subject, start teaching others either non-profit or for a fee, your choice entirely. This will help you to remain in touch of the entire course all the time.