To choose whether iTunes shuffles by songs, albums, or groupings, choose iTunes > Preferences, click Playback, and then select a Shuffle option. If you select Albums or Groupings, iTunes plays the songs in the order in which they appear on the album or in the grouping, and then chooses another album or grouping at random.
To adjust the likelihood that iTunes plays multiple songs in a row by the same artist or from the same album, choose iTunes > Preferences, click Playback, and then drag the Smart Shuffle slider.