The integration of pertinent literature into a scientific manuscript is a major key to a quality paper.  This requires a successful literature search strategy (this link takes you to a wonderland of library sources).

     When citing multiple sources within one set of parentheses, one needs to be consistent.  Some journals require papers be placed in alphabetical order by first author and others require chronological order.  Be consistent with the style that you choose to adopt.  As a result, a more appropriate way to list these two papers is:

     (Smith 1996, Tallman and Thorsett 1999)