World-Class Mahjong with World Champion Mai Hatsune (世界チャンピオン初音舞の世界に勝つ—麻雀国際公式ルール戦術本) is a book on the concepts and strategies in Chinese Official mahjong (COMJ) and is published by Hatsune Mai and Kajimoto Takunori. Hatsune Mai is the winner of the World Championship in Mahjong held in Tokyo, Japan, in 2002.
This book is the first and only book with an emphasis on COMJ strategy so far but it is in the Japanese language, which means many players around the world are unable to read it for its contents. Hence, an English translation of the content on strategy was made by Ryan Morris and is available online for everyone to read (link above).
This website on COMJ strategy will be most useful to beginners to COMJ. Due to the 8-point minimum for a win, beginners often have difficulties completing their hands. There are many helpful pointers on what to do when playing COMJ. There are detailed explanations of how to complete hands for a particular fan, such as Mixed Triple Chows or Mixed Shifted Chows; and advice on when to go for a higher-scoring fan like Pure Straight.
This website is definitely a good starting point for beginners, but even more experienced mahjong players can make use of the strategies, especially if they are not used to a pattern-oriented game like COMJ. For example, most Singaporeans are used to playing Singapore Style mahjong, which makes use of much fewer special hands and hand combinations than COMJ, and are thus unfamiliar with the various sequence-based combinations found in COMJ. Winning hands may be missed because of the player's failure to recognise valid winning combinations!
So, start reading!