Persuasion Principles

Liking: People like those like them, who like them.

Reciprocity: People repay in kind.

Social Proof: People follow the lead of similar others.

Consistency: People fulfill written, public and voluntary commitments.

Authority: People defer to experts who provide shortcuts to decisions requiring specialized informaton.

Scarcity: People value what is scare.

Source: HBRs 10 Must Reads on Communication