1. Study important frameworks
https://caseinterview.customerhub.net/page/videos
2. Ace the mental math
http://articles.submityourarticle.com/Richard-Jenkins-9110/mental-math-skills-170467.php
3.. Practice case interviews on McKinsey, BCG or Bain website

http://www.mckinsey.com/locations/Knowledge_Network/How_Do_I_Apply/Interview_Preparation/Case_Interviews/Great_Burger.aspx
http://www.mckinsey.com/locations/Knowledge_Network/How_Do_I_Apply/Interview_Preparation/Case_Interviews/Magna_Health.aspx
http://www.bcg.com/join_bcg/practice_cases/default.aspx
http://www.bcg.com/join_bcg/interactive_case/default.aspx
http://www.joinbain.com/apply-to-bain/interview-preparation/practice-case1-quest1.asp?stage=1&ques=1
http://www.joinbain.com/apply-to-bain/interview-preparation/practice-case2-quest1.asp?stage=1&ques=1
http://www.joinbain.com/apply-to-bain/interview-preparation/practice-videocase.asp
http://www.mckinsey.com/Careers/Apply/Interview_tips
4. Read case studies on company website
5. Play interactive games
http://www.mckinsey.com/locations/swiss/career/team_leader/index.asp 
6. Review these videos
http://www.consultingcase101.com/case-interview-videos/
http://www.youtube.com/watch?v=d-VgpMrFlIs&feature=related
  http://www.youtube.com/watch?v=NbxugyeU73A