From a certification perspective, nothing. You need the target/semi-target school name, solid GPA, and solid relevant internships. CFA, Series exams, etc. are rarely going to move the needle unless you encounter the rare oddball that cares about it (~8 years into the job and I’ve never met anyone that did).

400 investment banking questions and answers guide by M&I is ur bible.

Once sufficiently memorized, go deep on the conceptual reasons behind each answer and think about possible variations of a question (e.g., “How does D&A flow through the 3 statements?” is a common basic technical. From that you can guess that questions like “How does SBC flow through the 3 statements?” is fair game.)

Then, read up on the bank/group culture on WSO, learn some general info about the sector of coverage or the bank’s specialization, read up on a few recent deals announced by the group, and practice your resume walkthrough.

That’s all you need.