This is a simple demonstration of what makes the difference between a decent Scrabble player and a World champion. This position is taken from a game in this year's World Championships. It is the opening move, eventual winner, Nigel Richards is to go first, his rack is:
BCEOPSZ
Out of all the posible moves, the following is a list of the best:
BEZ
POZ
ZEP
COZ
BOP
How do we know they're the best? Well, serious scrabble players use a program to analyse their games that relies on simulation. Each position is played over a few hundred or a few thousand times by the computer and the top moves are evaluated depending on how many points they would expect to gain or lose over the next few moves. The difference between your actual move and what the computer says is best is known as equity loss. A high equity loss shows that you have played badly. Of course if you play the best move then your equity loss is zero. Sometimes spotting the best move is easy, sometimes, as in this situation it takes a genius's brain to work out all the options.
So why is BEZ best? Well on the downside, BEZ uses up a valuable E and it is generally useful to leave yourself with an E on your rack. Many players, me included would be tempted to play POZ or COZ for that reason.
However, Richards was clever enough to work out that playing BEZ and leaving CPOS on his rack gave him a better leave that the alternatives, (POZ leaves BCES, COZ leaves BEPS). Other factors also came into consideration such as playing COZ leaves a nice hook opening for COZE and ZEP and BOP also take -s hooks at the end.
Of course this one move didn't win the game but during the rest of that game Richards only dropped a total of 2 equity points and for the competition overall aveaged only 15 equity loss points per game. A standard that most of us can only dream about.
If you want to go through the rest of the game there is an analysis here
http://scrabblestats.blogspot.com/2007/12/wsc-finals-game-3-analysis.html