Before you go out and buy books, I would first recommend the stairways first.http://www.sqlservercentral.com/stairway/72399/

Then once you know enough, Gail's http://sqlinthewild.co.za/index.php/2011/11/11/sql-university-advanced-indexing-indexing-strategies/

Creating indexes is a multivariable mathematical problem in maximizing performance while minimizing cost so there is no easy get-rich-quick way as there are too many variables.