Placements occur in phases. First phase starts from December 1 ( called Day 0). Most of the companies visit the campus in this phase only. The written rounds are held, just beforehand to this time. Though, some conduct the written rounds just before the interviews. Though, some exception are made to this December rule for PSUs if they wish to attend any other time. Usually Day 0 is allotted to the highest paying companies ( atleast in CSE, for others it is not strictly followed ). So there are giants like GS, Uber, Flipkart , Amazon visiting on day0 itself.
Every company send their JNF ( job notification form) before visiting the campus, which is sent to all the eligible branches of the respective branches. Interested students send their names via Google forms created by the PRs ( Placement Representatives). These students then sit in the written tests. PSUs do not conduct written tests. They shortlist based on the CGPA. Every company have different procedures that lead to the interview processes. CS based companies mostly they are coding rounds while for core there are GDs or PPTs .Here is a pointer, selection from written rounds are not done exactly based on the merit. Sometimes companies don’t require the high securing students. They are seen to leave the company sooner cause they can create more opportunities for themselves. So they look for more stable sort of candidate.
The CS based companies mostly look for coding skills and soft skills do not matter much. For PSUs, speaking skills is one of the most important thing they look for. Other core companies look for both speaking skills and technical knowledge. Projects and training form the most important part in the interview processes. In the interviews, I think, what matters the most is how you present yourself there. Most of the technical questions are not head scratching. If you have read the subject and prepared some templated questions from internet, you can answer the technical questions. The HR questions is where you have to use your head. Prepare these questions very nicely. The companies not only look for a technical sound candidate but also who would stay in the company for sometime and not move at the first sign of a better offer from other companies.
For finance and analytics based companies the selection process go differently. They create various rounds to assess the financial aptitude of candidates.