When Rabbi Aryeh Kaplan wrote his book on "Jewish Meditation", the entire subject may have not yet been as popular as today. In our days, thousands of Jews are on the search for a more spiritual meaning in life. As I once learnt, every Jew has her / his own soul root. Thus many Jews are more interested in mystical subjects than others who rather prefer studying Halachot or Mussar. Each of us has a very different approach to Judaism including his individual task in life.
Meditation is already mentioned in the Talmud (Masechet Berachot) where it says that we should meditate before we actually pray. Getting into a certain mood and thus rid of our disturbing thoughts during prayer.
However, meditation is not meditation; meaning a Jew should practise JEWISH meditation and no strange variety of idol - worship meditation of other religions. The thing with Jewish meditation is that we have to learn it first and just do not sit down and run right into it.
From the book "Jewish Meditation" of Rabbi Aryeh Kaplan:
One of the first steps in meditation is learning how not to take our thoughts for granted. A simple exercise will demonstrate how difficult it is to control your thoughts.
This is the exercise: STOP THINKING !
Try to blank your mind for a few minutes and not think of anything at all. Sound easy ?
How long did you succeed in stopping your thoughts ?
A few seconds ? It is extremely difficult to turn off thought.
There is another way in which you can try to control your mind. Close your eyes and you will probably see flashes and lights. Give yourself a few moments to relax, and these flashing lights will subside and develop into a series of kaleidoscopic images in the mind's eye.
Now, with your eyes closed try to control these images. Try to depict the letter A in your mind's eye. Without any further practise, it is impossible to hold on to this image. This technique can be perfected only through extensive training.