If you cover both of your ears totally, you will hear your own heartbeat. That is the sound you are looking for here.
Start in a comfortable position, one you can sit in for a while.
If you have a hard time visualizing, a candle can be used to help keep your focus.
Start by blocking out all sound (you should already be in a quiet place) untill you start to hear that white noise that comes when your in complete silnce..
Let the tension start to flow from your head down to your shoulders, all the while listening for your own heartbeat.
Feel your shoulders tighten and then relax allowing all the energy and tension to continue to drain down. As you relax and continue to listen you should be able to hear your own heartbeat clearer and clearer. Dont worry if you hear it
and loose it, it may take more and more concentration to maintain hearing it.
Continue the tightening and relaxing to loose tension. Down your arms, tighten and relax. From your hands, tighten and release. In your stomach area, tighten and relese. Your thighs, tighten and release All the while feeling the tension flowing down.
When you get to your feet ,tighten and release and feel the tension flow out of your feet and away. By this time you should be relaxed and able to focus on your heartbeat, or at least be in a relaxed state. From this pont you'll find it easier to focus energy and visualize.