Starting with your opening play - The highest scoring word you can use as a first play, using all the tiles you have is MUZJIKS for a whopping one hundred and twenty-eight points. Two other words available in the international Scrabble dictionary are QUARTZY and SQUEEZY, which are both worth one hundred and twenty-six points apiece. As unlikely as it would be to get these exact tiles on your first play, they are scrabble words that are worth remembering for normal play.
There are five words in the North American Scrabble dictionary that are capable of an insane three hundred and ninety-two points each. These words are BEZIQUES, CAZIQUES, MEZQUITE MEZQUITS, and OXAZEPAM. To get the amazing point score for any of these words, the word needs to be spelled over two triple-word squares with a high-points tile on the double-letter score (e.g. a Z tile, Q tile, or X tile). This means playing the word at the side of the board, and connecting to an existing word. For this reason, points at this scale are generally rare.
In addition to these words, there are three eight-letter words which will can score up to three hundred and seventy-four points. These are Bingo words (7-letter words which can form another word with an additional letter). These words must be again played over two triple-word squares, with the highest available letter on a double-word square. The words are: HIGHJACK, WHIZBANG, and QUETZALS. Two other slightly lower scoring bingo words are QUIXOTIC and MUSQUASH, which score three hundred and fifty-size, and three hundred and thirty-eight points respectively.
Finally, the mother of all high-point words is the incredibly unlikely OXYPHENBUTAZONE. At fifteen letters long it would take up an entire side of the Scrabble board, and score an unbelievable one thousand, seven hundred and seventy-eight points. The set of circumstances required to make this word are so contrived that you have to be collaborating with a willing opponent to make it happen. In fact, in online games of Wordscraper you will see bored people trying to game the system by continually passing turns until they can make it happen for them.