First impressions in the C suite are critical. That's why Time Warner CIO Bill Krivoshik spent his first three months forging relationships with key stake holders at his new company. He also took a crash course in the media industry because he had never worked in it before and sought agreement among senior executives about the scope of the enterprise CIO role, which was new.
And he needed to gain an understanding about what capabilities Time Warner already had and which could be leveraged.
If you're just starting out, this Forbes piece is a good read as well as others in this series of first 100 days of other CIOs (see third paragraph).