Don't be afraid to exchange tiles sometimes. Nothing is worse than vowel sickness, especially if they're bad vowels like u's. Also - if you have a hand with at least 3 of the following: 'r,' 'e,' 's,' 't,' 'blank' -- there's a good chance you can make a bingo and tack the 's' or 'blank' to the end of an existing word on the board. There's no shame in skipping out on a 20 or so point turn to get a 70+ point bingo the next.
Know your leave. Your leave is what's on your rack after your turn. You don't want to blow all of your consonants in one turn - especially if you're not gaining substantial points -- this is the quickest way to get vowel sickness.
Never waste an 's' or a 'blank'. Neither are worth many points by their lonesome. Only use them if you're creating a bingo, opening up the board by pluralizing a noun that's already on the board, or in rare, rare occasions where they're necessary to get a high scoring tile on a triple letter (but even then, that's only if it's a desperate move - because most good tiles have easy two letter words that can get scored twice if placed properly). Don't unnecessarily pluralize words just for 1 additional point, please. There are so few 's's, and it hurts to see them wasted.
Know your two letter words. Every letter except 'c' and 'v' have two letter words. An 'xi' and 'ax' or something where the 'x' lands on a double letter and goes in both directions nets you 42 points. That's really not that bad of a play, especially when your chips are down and you need to get rid of that 'x,' 'z,' or 'k'.
Since 'c' and 'v' are the two letters without two letter words - prioritize getting rid of them if the game is nearing an end. Most other letters you can throw away easily in a last ditch effort - but you don't want to swallow the 3 or 4 points at the end if you can't get rid of either letter.
Open up the board - but not in a way that necessarily benefits your opponent. Yes - you don't want to build the board in a way that gives easy access to a triple word, or ideally even a double word. BUT if you're just playing 2 and 3 letter words the game will stalemate. You need to open up sometimes or else you'll have a frustrating game where you're sitting around forever waiting each turn (unless you're playing with a timer like competitive play).
You don't need to know what a word means to play it. There are plenty of common scrabble words that I have no fucking clue what they mean. Most competitive players memorize the dictionary, and admittedly don't know some of the words they commonly use. Just have a scrabble dictionary ready if you're playing casually.
Know the common 'q' without 'u' words, like qat, qi, etc.