Ever try to think of that one word that would fit a situation perfectly in your writing, but you can't think of it, no matter how hard you try, but you know it's out there? Yeah, I'm sure every writer has the same problem every once in a while.
The thing is, you can't really fix that. Instead, you have to find a word that will replace it almost perfectly. To do that, you need a big vocabulary.
Every day, I get an email from a dictionary site, telling me the word of the day, its definition, a few sentences it is in, and the background of how it was created. I try to memorize at least the word and its definition.
Then, later in the day, I make sure to use that word in my writing, one way or another. Sometimes, it's just a minor character walking by down the street, talking on their cellphone, but I still use it.
Later on, when I go back to read that, I'll probably wonder, 'what does that word mean?', and I'll go look it up, remember what it means, and then it sticks with me, more often than not, and I find myself using it more often in my writing, as it fits.