Many advanced level learners say that "けいご" (keigo - honorific speech) is difficult. This is common because most Japanese language schools don't allocate enough time to teach けいご systematically. 

But if you would like to learn けいご by yourself, then 新・にほんご敬語トレーニング will be of a great help! You can understand in what kind of situation you need to use けいご, and the book gives you plenty of excise of 敬語.

You can buy (or order) the textbook in Kinokuniya.

http://www.amazon.co.jp/%E6%96%B0%E3%83%BB%E3%81%AB%E3%81%BB%E3%82%93%E3%81%94%E6%95%AC%E8%AA%9E%E3%83%88%E3%83%AC%E3%83%BC%E3%83%8B%E3%83%B3%E3%82%B0-%E9%87%91%E5%AD%90%E5%BA%83%E5%B9%B8/dp/4872178564