What are the criteria for the best move in Scrabble?
Any move in Scrabble has a few effects on the game:


It earns you points.
Unplayed tiles remain on your rack.
You draw new tiles (usually).
The board changes, which can make scoring easier or harder.


This suggests that the best move is one that can maximize as many of these (sometimes conflicting) aspects:


It scores a bunch of points.
It leaves you with complementary tiles for future points, especially having a good vowel-consonant balance.  It often pays to forego a few points this turn for a good opportunity at a bingo the next turn.  
It lets you draw many tiles.  This means more opportunities for getting "lucky" with high point tiles (JXQZ) or super useful blanks.  
It shapes the board in a way favorable to your current gameplan.  The best advice I've heard is to open the board up when behind (for more opportunities to catch up) and to close the board down if you're ahead (for just the opposite reason).  


You won't always have an obvious best choice, but the more bullet points you can achieve the better.  Bingos are especially important because they score a bunch of points and give you more chances of drawing important tiles.