WWF scoring is different
Words With Friends does not use standard Scrabble values for every tile. That means the same word can have a different base score before any premium-square bonus.
Do not hoard power tiles
Holding a valuable letter for too long can damage rack balance. A clean scoring opportunity now may be better than waiting for a perfect triple-letter setup that never appears.
Score and leave both matter
After comparing the immediate points, look at the tiles left behind. A slightly lower-scoring play can be stronger when it produces a balanced next rack.