Summarising this post by Tim Challies:-

1. False teachers are man pleasers.  They deal, not in what their hearers need to hear, but in what they want to hear.  See Gal 1:10; 1 Thess 2:4.
2. False teachers oppose God’s most faithful servants.  So it was that false teachers dealt so brutally with our Lord himself.
3. False teachers teach their own ideas, rather than God’s word.  See Jer 14:14; 23:25; 29:9.
4. False teachers neglect what is of greatest importance in order to focus on what is less important.  They will stress lesser commandments over greater ones (Mt 23:23), and minor matters over essential truths.
5. False teachers mask false doctrine with eloquent speech and impressive argumentation.  They cover their poison with honey.  See 1 Cor 2:1.
6. False teachers are more concerned to win people over to their own opinions than to win them over to Christ and the gospel.  See Mt 23:15.
7. False teachers exploit their followers.  They do not seek their good, but their goods: their loyalty, their admiration, their money.  See 2 Pet 2:1.