Time Magazine's films Novak Djokavic providing lessons on all strokes of the game. Djokavic provides tips on the forehand, backhand, serve, drop shot, and overhead.

Suggestions of how to learn and practice the tennis drop shot - from www.WebTennis24.com

Great instruction from Tennis.com about the drop volley. 

This articles is great for players who are beginning to play matches and are building control on shots. The article lays out what exactly a drop shot is and some advice on how and when to use it.