Having just finished a round of copyediting and proofreading, I feel like I've learned some valuable lessons that I should pass on.
One thing is that it's a really good idea to give the near-final version of your book a quick read -- reading as much as possible in as few sittings as possible. That will make overused words and phrases pop out at you. If you read a word or phrase once in a reading session, it's not so bad. If it pops up multiple times, you start to notice. If one does catch your eye, do a global search and you may be surprised how many times it comes up.
Fixing this may not just be a case of using your thesaurus. There may be another issue at work. For instance, in a recent book I was working on, the phrase "as though" and the word "seemed" jumped out at me. At first, I started changing some of the uses of "as though" to "like" or "as if," but then I noticed the "seemed" overload and realized that I was using weasel words. I was trying to avoid breaking point of view by having it "seem" to the character what was happening when the character couldn't get into the other person's head to know for sure, but I'd gone overboard. There were plenty of cases where it wasn't "as though" something was true or even that it "seemed" it was true. It was just true. Or I could find another verb. Instead of saying "It seemed as though she was tired," I could say "She looked tired." Or I could describe the way her feet were dragging, her shoulders sagging, her eyelids drooping, etc.
Another way to catch this sort of thing is to read your manuscript out loud. Your eye may skim over things like this, but when you hear it said out loud, it will be a lot more obvious. As a bonus, when you read out loud, you have to read every word, so you know what's really on the page instead of your brain filling in blanks or fixing things for you. It's also a good way to check awkward phrasing and to make sure your dialogue sounds like actual human speech.
I think a lot of this becomes more important if there's a chance that your books will become audiobooks. When you listen to a book, you hear all those words that you may skim past when you're reading. I've listened to friends discussing audiobooks and how they can't listen to the work of some authors they enjoy reading because of verbal tics that get annoying when reading out loud. For instance, the use of the word "said" for every dialogue tag. One oft-repeated bit of writing advice is that you shouldn't use fancy synonyms for "said" (uttered, shouted, declaimed, etc.) with dialogue because "said" is an invisible word. It's no longer invisible in an audiobook, and the repetition gets annoying. In some cases, such as a two-person conversation, tags aren't necessary for every line. You can use action to indicate who's talking. And those synonyms sometimes actually work.
Of course, the more engrossing your story is, the less likely it will be that someone will notice minor flaws. But you don't want to give any reason to pull readers out of the story.