I can't stress how much your vocabulary can improve your writing. Have you noticed how much you've been using that word(s) lately? Have you written hundreds of words, only to scrap the whole draft because it doesn't reflect exactly how you imagined it.
Well this is probably cos of your lack of vocabulary, so to improve it what does that mean? Improving it is going to help your writing immensely. A better word instead of the word you've been meaning to use can do wonders. And that's just one word, imagine whole sentences? paragraphs?
So how can you improve your vocabulary? Well simply you just gotta learn new words and their meanings. Practise using them. And finally implement them into your stories. It'll make it much, much more easier to display your imagination. A quick way to scan through your stories for a lack of vocab is using the Cntrl + F method (Cmd + F for mac) to find words in tour stories. The Thesaurus is basically your best friend when you're writing stories, it'll provide so many ways to replace words you use.
But is that enough? No of course not, replacing single words isn't going to help much, it'll be a good start, but the sentences are still the same. Learn to use different structured sentences, and different combinations of words from your vocab.
Even if you think you have enough vocab, you don't, there is an endless amount of words you can use in for writing, and it means you can endlessly improve your writing.
Another thing, the word "very" should be banned, there are so many different words you can use instead of very. Very big? Enormous/Gigantic/Colossal . Very Hungry? Famished/Ravenous/Starving . Very Old? Ancient/Prehistoric/Primitive . Very Strange? Queer/Peculiar/Bizarre
Use that thesaurus and avoid very.