From Dennis Prager:
Without the belief in an ever-expanding state, there is no Left. Without a belief in limited government, there is no conservatism. Moreover, understanding this difference is essentially all people should have to know in order to determine whether they are on the Right or the Left.
The Left believes the state should be the most powerful force in society. It should be in control of educating all of its children; it should provide all the health care for all of its citizens; and it should supervise just about all other areas of society. There should be no competing power. As to the all-important question of how much government is too much government, I have never encountered a person of the Left who had an answer to that question.
Conservatives believe the individual is the essential component of a good society, not government. The government’s role in society should be limited to absolute necessities such as national defense and to serving as the resource of last resort for citizens who cannot be helped by other citizens, private organizations or charities that donate money and time.
Source: It’s All About Big Government Left-Right Differences: