The first step in the journey of getting a Ph.D. degree is giving either of these exams; GATE, NET, CSIR, or UGC. Next, you have to decide on a particular field in which you will be conducting your research. After this, you have to look for a faculty advisor that has experience in the kind of research work you are looking for. His teaching style should necessarily align with your learning style. Conduct extensive research on the topic you will be working on. 

IIT Bombay: Here, you are required to do some coursework on the topic you have chosen. Choose the course that will give you more opportunities than others. Most Ph.D. students take some courses only to make up the required credits. This is not right as you will miss the opportunity to learn so much from every department. The most preferred courses are CS and Modelling at IIT Bombay.

One can even upgrade their skills in Mathematics and Statistics. Other courses that might help you in research work are fluid mechanics, soil mechanics, inorganic chemistry, solid-state physics, and thermodynamics.

Basically, you should choose your coursework not only for credits but to get knowledge of the research work you will be doing. Seek help from your advisor on the same.