2. Learn Data Structures and Algorithms

Once you are comfortable with any of the languages mentioned in the above section, the next thing you should do is learning data structures and algorithms. Data structures and algorithms help in building the right aptitude required for programming. Knowledge about the data structures will help you in choosing the right one for the problem you are solving - not all data structures can be used everywhere. When you learn about the algorithms, you will be able to understand the working mechanism of many library functions, which, otherwise, would come across to you as black boxes.

There are many good online courses that you can study from. Algorithms part 1 and part 2 are good courses to start with. It is important that you spend time thinking about the implementation of these data structures and algorithms so as to get comfortable with them. You may think that learning their implementation might not be important as ultimately the library functions are used. This is one of the most common misconceptions people have. Understanding the implementation will help you in assessing the time complexity, which will help you in further optimizing your code. There is an amazing website, Visualgo, where you can actually visualize the working of the various data structures and algorithms.