First of all, congrats on getting selected in SBI clerk recruitment written test.
The personal interviews are to start from December 8, 2014
Marks: Candidates are required to score a minimum percentage marks in interview to be considered for final selection. 5% relaxation for SC/ST/ OBC/PWD/XS category will be available)
The minimum marks to score in interview will be decided by SBI later & hence you wont know it now.
Preparations: Since you are appearing for interview in SBI, make sure you know about the State bank of india.For this, go to their website & know about their ogranisational structure, no. of branches, name of chairman etc.
Then learn the banking terminologies so you dont blink when the panel asks questions about the NEFT, Credit cards, functions of RBI or questions similar to that.
To know about banks, commonly used words in banking industry & how to answer some of the top interview questions, checkout this book:
Buy Interview Cracker (crack bank interviews with answers for top questions) for Rs.105
Concentrate on the latest current events that is happening or that had happened in the last 6 months.Read business newspapers or atleast the headlines to you dont miss the important activites.