A planting hole for a new climber or wall shrub should be at least 5 in. larger than the diameter of the root ball and deep enough for the base of the stem to be level with the surrounding soil. Clematis should be planted slightly deeper, because it is susceptible to wilt. If this happens and the plant is deeply planted, it may grow again from the roots, so do not dig up an apparently dying clematis plant for at least one season.
Give the young plant a supporting framework and tie the leading shoot in to this to persuade it to grow in the direction you want.