Why you should read Essentials of Bid'ah by Shaykh Khalid bin Ahmad Az Zahraanee:
Learn the lexical and juristic meaning of bid'ah (religious innovation)
Understand the evil effects of bid'ah
Discover the words of disparagement that the Quran and Sunnah use to describe bid'ah
Learn about the different categories of bid'ah
Understand how to deal with the people of bid'ah
This book is essential reading for anyone who wants to learn more about bid'ah and its dangers. It is also a valuable resource for those who are involved in dawah (inviting others to Islam) and who may encounter people who are following innovations.