Venkat, there is a
Marketo Certification Program page that has some info about this. The key to success is to be actively using Marketo for many months (the page recommends a year). There are some questions about Admin and Reports, which you may use less frequently than other areas, so be sure to review that. There are so many Marketo help articles, it's hard to point at one definitive set of material. You may want to invest in Josh Hill's
Marketing Rockstar's Guide to Marketo, which is a comprehesive review of Marketo's functionality.