Before we were locked-down, you might have traveled along a familiar road, perhaps a daily trek to work or to the supermarket, and not remembered the journey when you arrived. It was probably easy and pleasant and left your mind free to wander, but did you notice anything along the way? If someone was to ask you for directions to somewhere on the route, could you tell them whether it's the second or third turn on the left, opposite the postbox or past the big iron gates? Probably not.
As with well-worn paths, so with writing. It's easy to fall into using the same style and structures without even noticing. What you write can become like yesterday's reheated leftovers–okay, but boring. How can you alert yourself to limited vocabulary, repeated phrases or awkward sentence structures?
A good way to start is by using your computer's proofread facility, if it has one. This will offer you alternatives to convoluted phrasing. Doing a search for certain words you think you might be overusing is also a good idea. It's hard to recognise your own bad habits, so a beta-reader or, if you can afford it, a copy-editor should spot the repetitions you miss.
Setting yourself strict word limits helps you identify words you don't need. Exercises such as writing a paragraph only using words starting with the same letter will help you bring out vocabulary that's stored on the dusty shelves of your memory. Finally, read as much as you can taking note of how other authors tackle narrative, descriptions etc.. Don't worry that you'll copy or plagiarise them. The idea is to defamiliarise writing to make you more aware, so that you look at your own work anew, and arrive at The End refreshed.