Keep your weight on the balls of your feet, not your heels.
Pay attention to the various sensations coming from your soles--both for safety and stimulation.
Try to walk barefoot on as many surfaces and textures as possible to sensitize your bare soles. A well-developed sense of touch is important, both for safety and for enjoyment.
Be careful when you cannot see the ground because of grass or leaves. Step lightly and carefully under these conditions.