You must simply place a word over a TL (Triple Letter) or DL (Double Letter) and over a TW (Triple Word) or DW (Double Word)
The easiest way to do this is to clear your rack and hit the DL and DW spaces in one go. (Also if you have not used all your letters in one turn to make a word you will also receive the 'Bingo' Achievement.
(This can be done in 'Pass & Play' Mode)