Approach the wall at a reasonable pace.
Place your foot that is closest to the wall on the wall first at about thigh height.
Move your second foot on to the wall about half a yard in front of the first because it's harder to stay on the wall if you
take large steps. Also use your arms to try and maintain balance.
In this tutorial my landing from the wall is very un-parkour like, i would suggest thrusting off the wall with your foot
that remains on the wall. With practise you can get some good height off this method and possibly use it to clear railings.