My brother is an alumnus of IIT Madras and here are some tips from him for doing well in placements.

• For the placements, the algorithms are much more important than the language. You can pick just one language like C++ or Java.
• You can learn data structures and algorithms. Various questions are asked from topics like linked lists, binary trees, queues, stacks, etc.
• It is also important to choose the language depending on the sectors that you are targeting. If you are going for analytics/data science profiles, it would be better for you to learn R and/or Python. Along with this, you need to be strong with the basics of statistics.
• If you are good at maths and know one of these languages then you are good to go.

Hope this helps.