There are several types of coaches working with the top pros on the ATP and Sony Ericsson WTA Tours.  Some coaches have been Grand Slam champions themselves, e.g. Tony Roche who helps Roger Federer and Jimmy Connors who is with Andy Roddick.  Other top level coaches played on the tours, but are not Grand Slam champions, e.g. Brad Gilbert with Andy Murray, Loic Corteau with Amelie Mauresmo and Larry Stefanki with Fernando Gonzalez.  Then there are the family coaches such as Venus and Serena Williams' parents, Rafael Nadal's uncle, etc.  In addition, there is the legendary Nick Bollettieri who has worked with many pros from Monica Seles to Andre Agassi to Tommy Haas.  Robert Lansdorp trained many very successful pros such as Tracy Austin, Pete Sampras, Lindsay Davenport and Maria Sharapova in their early years, but rarely traveled.  Clearly, the level of on-court success and formal tennis coaching training varies enormously between these successful coaches.  So what makes a great coach?  It has to be someone who understands the particular player's technique well enough to offer tips when strokes go off slightly.  A coach needs to be able to help a player strategically focus on his/her strengths while covering any weaknesses.  Most, but not all, top coaches scout future opponents.  Finally, a coach needs to understand what to tell a player at different moments to bring out the best performance.  As Oracene Price (Serena Williams' mom) and Tony Roche, coaches of the 2007 Australian Open winners have shown, there is no one "right" path to coaching success.