Tom Davis' "The Mathematics of Sudoku"
Read Tom Davis' paper, paying special attention to the way he names the cells and to his development of language. Next, if you have not done Sudoku puzzles before, Web Sudoku and Daily Sudoku and are two popular sites. Do one or two before moving on to Ken-Ken.
Click http://web.archive.org/web/20160304185502/http://www.geometer.org/mathcircles/sudoku.pdf link to open resource.