Samson, I have a question.  Where should I contact most of the balls – when the ball is rising, when the ball has reached the peak in the trajectory, or as the ball is falling?
 
 
 
Good question.  I’ll give a separate answer for each stroke.
 
When blocking, it is important to contact the ball on the rise; this will help you to keep your block low and give your opponent less time to react.
 
When smashing topspin, you should usually contact the ball at the top of the bounce and smash forward and down using some topspin.  If the lob hits deep near your end-line, then your smash will be more forward.  If the lob hits near the next, then your smash will be more downward. 
 
When smashing backspin, you should usually contact the ball on the top of the bounce or as the ball is dropping slightly.  This time, your angle will be more open and you will need to possibly lift slightly as you smash.  Also, you should adjust your body position closer to the table.  A high backspin lob will tend to stop over the table or even float back to your opponent slightly.
 
When looping backspin, you should usually contact the ball on the top of the bounce or as the ball is dropping slightly.  Professional players usually loop the backspin fairly early and beginners usually loop the backspin later. 
 
When looping topspin, you can loop the ball on the rise, on the top of the bounce, or on the fall.  When playing the ball quick, the timing is very important.  You should be ready to adjusting quickly with your feet, shorten your swing slightly, and focus on adding spin to the ball.  When letting the ball drop more, you should lengthen your swing and add more body to your swing.
 
When pushing, you should contact the ball on the rise so that you have the option of pushing long or short.  By taking it early, you will also be able to keep it low and use the angles as well.
 
When flipping, you should contact the ball on the top of the bounce or very slightly after the top of the bounce.  Move quickly into position, pause slightly, and flip with good spin to a tricky location.  Because the distance is so short between your contact point and the opponent, you can probably trick him if you use some strategy in your placement.