The best time to plant clematis would be Spring, Summer, or early Autumn in a location of 5-6 hours of sunlight.
Loosen the soil to a depth of 2 feet. Mix this soil with peat and sand. Carefully set your clematis plant in the hole so the crown is 1 inch below the soil level when the plant was in the pot. You will cover up one or two sets of leaves. You do not need to remove the leaves. Shoots will appear from under the ground from these nodes that are covered with soil, creating a bushy plant from the base. Also if the plant is ever broken off at ground level it will not be lost as it will shoot up from under the ground.