For PhD with a science/engineering background at a target school, the process starts with on campus recruitment. Getting an interview largely depends on the quality of the resume, which should really stand out as they probably spend no more than 30 sec on each in the screening process. Previous internship at Fortune 500 companies is (almost) a must as there are more people with it than they recruit. PhDs are hired at the same level as MBAs so the competition is fierce. There are two rounds of interviews and most people get cut in the 1st round. Interviewee driven style for cases so if you don't get to the point they will just stare at you. At least 3 months of preparation is necessary, but you can spend a year to prepare and still get cut in the first round, which happened to tens of people I know. Don't get obsessed in this. Luck is most important.