I focus on the area,and i give the mental command to ''let it drop''to the ground.

At first you can try it with your hands..

Say in your mind ''i let my left hand to drop down''.

Let your arm to ''let go'' completely and feel the gravity of the earth pulling it down..(You don't do it,you just let it happen.)

Your arm will start to feel heavier,and you might experience something like a tingling-numb sensation..
You can do it even while you walking..

The key is to allow it to happen without trying to force it...The mind can do a lot of things,but you have to stay somehow out of the process.
That means that you give the commands,but you let your inner self to do it...