Wait until early winter to prune. The Virginia creeper loses its leaves and goes into dormancy, making the stems easy to measure and trim.
Cut off any dead, diseased or insect infested vines. Inspect the plant for vines torn loose from their support and cut off the loose vines. They are not able to reattach themselves to the support.
Cut back any stems growing outside the bounds you designated for the plant. Cut the stems back to the height you desire. Always make the cuts with sharp pruning shears, just above a leaf bud.