function showTip() {

  var randomNumber=Math.random();

  var whichTip=Math.floor(randomNumber *  19 ) + 1;

  var tip = new Array(19);

  tip[1]="Turn your body sideways on your backhand.  By doing so, you have already started to take your racquet back in preparation to hit the ball.";
  tip[2]="To hit a low volley, try not to bend at your waist.  Keep your upper body straight and upright and bend your knees to get down low to the ball.";
  tip[3]="When preparing for the next shot, hold the throat of your racquet with your non-hitting hand.  Then you can use it to turn your racquet for your quick grip change.";
  tip[4]="Trying to generate spin on your groundstrokes?  Take a good look at what grip you're using.  Changing between Eastern, Continental, and Western grips makes a world of difference.";
  tip[5]="Be sure to follow through on your strokes.  A proper follow through adds power and control to your shots.";
  tip[6]="Pronation is key on your serves.  The inward rotation of your hitting forearm as you serve is what gives the ball that extra spin.";
  tip[7]="Stay down low for your shots.  Having a low centre of gravity allows you to be balanced so that you can execute your shot correctly.";
  tip[8]="When you're in trouble throw up a defensive lob.  Trying to go for a winner when scrambling to return a shot is a low percentage play, a lob will keep you in the point so you can hit that winner later.";
  tip[9]="Do you recognize if your opponent is left handed?  If you are aiming into the ad court hoping to take advantage of a weak backhand, you may be hitting right into their stronger forehand side.";
  tip[10]="The power of the serve comes from your legs, not your arm.  Don't try to muscle your serve in, bend your knees and thrust your body up into the ball from your legs.";
  tip[11]="In Singles, approach down the line.  When trying to get into the net for a volley, hitting crosscourt leaves too many options for your opponent to pass you.";
  tip[12]="In doubles, hit your groundstrokes crosscourt and away from the net player.  This is the best percentage shot during a rally if both teams are playing in the one up / one back formation.";
  tip[13]="In doubles, when volleying, try to aim your shot at the feet of the opposing net player.  This play puts them in a defensive position and even if they manage to get the ball back, it will be a high sitter for you.";
  tip[14]="In doubles, the partner with the stronger serve should elect to serve first.  This is because this partner will be serving more often during the course of the match just because of the way the scoring system works.";
  tip[15]="In Singles look for your opportunity to come in off a short ball and be in a good position to put away a winning volley.";
  tip[16]="Playing with someone at a lower level?  Make it competitive by playing with a handicap.  For each game, start down by the number of points that you are games ahead.  If you are up by 2 games and the set is 3-1, give your opponent a 2 point lead and start the 5th game down 0-30, and continue.";
  tip[17]="To work on your depth consistency, try a co-operative rally of 10 straight balls where you hit manageable shots to your opponent, but make sure the ball lands between their serviceline and baseline.";
  tip[18]="Aim your smashes deep or shallow depending on the spin of the lob.  Aim your smashes shallow against topspin lobs.  Aim your smashes deep against underspin lobs.  This compensates for the spin of the lob.";
  tip[19]="Extend your non-hitting arm and point at the ball when preparing to smash a lob.  This automatically puts your shoulders in the correct position and helps you track the ball for the timing needed to hit a smash.";
  
  document.write(tip[whichTip]);
}