They include mood, group size, authority, and social approval.
People use conformity to ingratiate themselves with others. Conforming also makes people feel better about themselves by bolstering self-confidence. Some people have a greater need for liking from others so are more likely to conform.
Have you noticed that nonconformers are less likely to care what other people think of them? Nonconformity and self-confidence go hand-in-hand.