Think about how we generally (but not always) consider adverbs indicators of weak verbs. In those instances, adverbs are breadcrumbs. In an individual's writing, breadcrumbs are usually specific words or phrases rather than a general class of words. Action words applied frequently to multiple characters can be breadcrumbs. Sometimes they are your scapegoat words--the ones you turn to when you can't think of a new way to say the same thing. A thesaurus is an excellent writing tool, but if you find you're looking up the same word over and over, that word is your breadcrumb.
Critique groups and first-draft readers are great resources for identifying and defining breadcrumbs. When they tell you a certain word is getting repetitive, think about why that word is there and ask them what it does or doesn't do for the story. This is how you figure out what weakness your breadcrumb indicates. Sometimes repetitive words are just repetitive words, but a quick assessment before pulling out the thesaurus can make editing and future projects more productive and less frustrating.
One of my breadcrumbs is smiling. When my characters smile or grin, it usually means I'm not paying enough attention to my characters' personalities or that I haven't fully developed them. Smiles indicate a range of emotions from plain old happiness to amusement to nervousness. When my characters are well-defined, they have much more specific ways of showing those emotions than with a smile. A smile is the first thought I have as to their reaction, but instead of thinking about the character's physical reaction, I should first think about their emotional reaction. From that, I should determine a physical response that is more closely indicative of the emotion.
When you've figured out your breadcrumb and what it says about your project, it will help identify and eliminate problems earlier in the writing process. Once I recognized my issue with smiling and realized it meant my characters weren't yet three-dimensional, I could pick that up early on in other projects. My characters still smile, but when I notice I have a page full of smiling people, I know that I need to stop and spend some time developing my characters outside the story before moving further into the plot.
Knowing your breadcrumbs eases the editing process for future works as well as current ones. In completed projects, you can simply run a search for the word or phrase and determine its effectiveness in each case. In future projects, you'll be aware of it throughout the writing process. When it starts popping up, you can pause and determine what flaw is causing you to fall back on that word.
What are your breadcrumbs? Need help figuring out their meanings? Tell me about them in the comments.