Begin by sitting quietly and focusing on your heart.
Imagine yourself drawing in the energies you've given out today. Pull back the energy that has gone into chatting, encounters at work, the distractions of shop windows, or the emotional pull of others.
Don't worry if you don't feel you're fully able to do this. Above all, don't worry that this will cut you off from the people you love. On the contrary, the practice will let you gather your forces to meet them from a more centered place.
Now imagine a circle of protective energy around you. One way to do this is to visualize a thick ribbon of light emanating from your heart and wrapping itself around your body like a cocoon. See this light ribbon as an energetic shield that lets in energies that belong in your field and keeps out energies that don't.
Now, with your awareness in your heart, begin to focus on the breath as it enters and leaves the body. Imagine a window in your chest wall, and the breath flowing in and out through it. With each inhalation, have the thought "I am that I am." Or you may shorten the mantra to "I am." With the exhalation, sense the I-am in your heart center.
Let this pure thought, the recognition of your pure existence, center you and draw you deeper inside. Think of this practice as an exercise in meeting your invulnerable core. It will give you the strength you need to open to your own vulnerability without being overwhelmed by it.