The basic insights of classical liberalism were developed in the late 18th and early 19th centuries. They are:
The goal of life in this world is happiness, human flourishing, and wellbeing. Opposing views are that the goal of human life should be something else such as: storing treasure in the next world, serving the ruler, seeking glory, or a whole range of other things.
That personal choice and, hence, individual liberty are crucial in explaining both how society develops and in the achievement of individual happiness and flourishing.
That commerce, wealth, and trade are good, while war and conflict are bad. Opposing views are that war brings out the finest qualities in human beings and that wealth is actually bad for people.
Individualism: That people are distinct, separate, and self-governing.
Spontaneous order: That much of the order and structure we see in society is not the product of conscious design, but something that just happens when the right kinds of institutions and rules are in place.
That things can and will get better for society over time.
Reason, rather than tradition or authority, is the way to understand the world and make sense of it. Use reason, empirical investigation, and study to understand the nature of the world or how human society works; not rely on sacred text or blindly accept statements of authorities.