Create precious boost tiles with four-letter words, and cuss words are okay.
Excluding singular and plural forms, you can only spell a word once in a level, and after that it will cost you a move but not help you. Misspelled words produce the same effect.
Let letters stick around long enough and they gradually gain point value, thanks to multipliers.
Look at point value, not length of word. Shorter words can often net you higher scores.
Try to use square and stone tiles first, since you'll have to include them in a number of words to break them.