The Fourth Pillar [of Promoting Virtue and Forbidding Evil]: It has stages and mannerisms.
The First Stage: To know the evil [i.e. to seek knowledge and educate oneself about the specific evil act and know the evidences before embarking upon forbidding it].
The Second Stage: To familiarize the person with the evil act [i.e. to educate the person practicing the evil about it].
The Third Stage: To embark upon forbidding the evil by counseling and advising in an encouraging manner [i.e. to encourage someone to forsake an evil act by quoting evidences that encourage him/her, such as mentioning the rewards for forsaking the evil act. ]
The Fourth Stage: To embark upon forbidding evil by citing evidences that scare and warn a person from committing it [i.e. citing the evidences for the punishment of the act.] 
The Fifth Stage: To be harsh and use harsh speech in forbidding evil.
The Sixth Stage: To change an evil physically, such as breaking musical instruments or spilling alcohol [This stage and those following it are only for an individual who has the authority to do so as is well known with Ahlus-Sunnah, such as a ruler of a country or a parent at home.]
The Seventh Stage: To warn and scare.
The Eighth Stage: To physically discipline the individual.
The Ninth Stage: For one [ruler] who is unable to embark upon it on his own and needs supporters with weaponry. [i.e such as a war between nations.]
_____________________________________  The third and fourth stages are one in the original Arabic text, they have been split here to bring further clarity to the stages as has been explained by some of the people of knowledge. All comments in square brackets are the words of the translator, benefited through a class on the topic. A full explanation of the text will follow inshaAllah which will replace the comments when a suitable one is found.