To really be great you need both word knowledge and strategy, because not knowing words (especially hooks!) can make strategies useless.
Good strategies to pay attention to for a minimum are
- Tracking at the end of the game to know what the other player can do, even approximately
- When you're ahead, try to minimize the easy bingo lines. It's not hard to prepare for that.
- Adjust your play for when the board is open or closed. At least pay attention to whether there are a lot of bingo lines etc.
- Try not to keep ridiculous bad combinations of tiles in your rack after you play your word. Consider hoarding an S or a blank or a Z for a turn to get a better score (sometimes I do this way too much)
- Time management, not to be too low on time at the end of the game.
I think I do most of these things naturally. I find it very difficult to learn all the words length 6-8 even. My rating has been 1550-1700 consistently.