We all have particular words that we like for whatever reason. When we're trying to describe something, they are the first words to pop into our minds. Maybe it's a noun like "rage" or a verb like "devour." ("Dart" pops up a lot for me.) Or maybe it's an adjective or a phrase that we fall back on to describe a person. I don't worry about this while I'm writing. I wait until I pick up my red pen when I'm editing to locate and replace my comfort words with ones that are more interesting.
When you're editing your work, be on the lookout for characters that refer to something exactly the same way. For example, how likely is it that two or more characters will all describe the same event as a "hassle"?
Also, try to avoid the dreaded "gots." Too often, several characters will use this construction repeatedly, saying "I've got to get going," "I got the catsup," "I've got to pick up the mail," and "I got tired." (Me too after wading through page after page of that.) The "gots" make it tough to differentiate between individual characters and the narrative voice. They also prevent you from using stronger, more active verbs.
Content can be repeated as well. Sometimes a writer is afraid that readers won't get something, so the writer hammers home a key point many times. I once edited a book where the need to earn a character's trust was mentioned 26 times in one chapter. That's a lot of trust. In cases like this, trust your readers. Try to say something only once, twice if you absolutely must or if many pages have passed since the first mention. Whoever serves as your beta readers -- friends or family or writing group members -- will quickly let you know if they can't follow something in the story.
When you're reading your first draft, be alert for repetition of words, phrases, or content. Circle them as you go and fix them later when you're editing your work.