You may be challenged, but if you study the 'q' section of an official Scrabble dictionary long enough, you should know which words will hold up to the challenge. The same goes for a lot of other obscure words that will help you dispose of letters faster in the end game. One infamous example is 'aa', a form of lava. By carefully studying a good dictionary, you should be able to uncover quite a few words that will get you out of a jam. Avoid 'eieio' at any cost.
Many Scrabble players are reluctant to exercise their right to discard unwanted letters.
Since the rules indicate that such a move will end the player's turn, many beginning players assume that a missed turn is a bad thing. Experienced players realize that you sometimes have to cut your losses in order to be in a better position later in the game. A tray filled with nothing but vowels will not give you much more of a tactical advantage than sacrificing a turn for better letters. A tray filled with nothing but consonants is not exactly a winner either, but you should carefully consider which letters to dispose of and which to keep. Never throw away an 'S' or a 'D'- these can usually be played all the way through a game.