Boy did I make a booboo in a Scrabble game yesterday, and I had to fight hard to come back and take the game. It's one of those somewhat obvious things, but at the same time, I thought I'd mention a couple of specifics that made my move particularly bad.
The generally bad choice I made was to run a word up vertically to the top left of the board so that my top tile lay between the 2 triple-word-score (TWS) tiles, both unplayed. We know that this opens up an enormous turn for the opponent -- if he can play a BINGO in addition to your tile, he can hit both TWS spots for a 9X turn.
What made my play really bad is that my top tile was the letter R -- an easily useable tile -- AND ... we were more than halfway through the game with NEITHER blank showing up. My opponent had both, played something through my R onto both TWS tiles, and scored 131 points.
If you're going to play into the middle of 2 TWS spots (both unplayed), keep in mind that: 1) it had better be a very good play if you're going to take the risk; 2) try not to play tiles (between the TWS spots) that are easily used for your opponent's word; 3) consider how likely it is for your opponent to have blanks, S tiles, and other easily used tiles.