I guess you already know what to do the mental simulation
because I believe you have already used it in your daily life. Perhaps
you just do not aware of it or do not use it often. If you really
do not know how to do a mental simulation, here is a simple practice.
Start with seeing any object near you and look
at it carefully. Close your eyes and see that object in your mental
vision. If you fail to see, take some time and open your eyes and
look again that object. Repeat this step until you can see the object
in your mental vision. These step is to use your mental vision to
see static objects.
Then you can improve to dynamic object. You look
at other person you know near you and then close your eyes and use
your mental vision to see what they are doing now. Again if you
still fail, you can open your eyes again and look carefully what
are they doing and repeat this step until you can see clearly in
your mental vision their movement.
Now improve your mental simulation to see using
your mental vision what other person that you do not see with your
own eyes. Imagine what they are doing and make a film in your mental
vision about it.
Repeat these steps toward other person and objects
until you can see clearly in your mental vision about anything you
want to see. More practice will make you see better and clearer.