I'm not sure I'm always the right cup of tea for someone, but I would love to help any way I can.
Personally, I find it easier to learn from someone when roleplaying. It's where I feel the best situated, to examine a writing style and what can be improved on, or used to examine a skill. Particularly, it helps when you can point out in a developing story what consistencies are in your writing, and whether or not they can be improved on.
Aside from my philosophy of teaching, something that I can suggest is to try using prompts. Personally, if I am forced to think about writing something in a different way, I come up with something I probably wouldn't have, had I written about the same thing without parameters. One specific thing to increase vocabulary, besides reading more, is to study stems of words, and google vocab lists as ways to suss out new words. (Also, I find that using thesaurus.com whenever I feel like I'm becoming so redundant it's almost painfully obvious, I find new words to use, besides just the ones associated with the word I was looking up.)
Sentence variety and phrase/fragment variety is somewhat of a challenge to most people, simply because it is heavily rooted in grammar. Though I'm not the most spectacularly diverse, I try to use my knowledge of the English language to my advantage. I sometimes like to think that the best sentences are often written as they would be spoken; though how things sound and are written for spoken word is much different and should never be interchangeable, it does lend a nuance to the writing. A specific tone and voice, if you will.
Uhm, I guess that's all I can say. If you'd like to spend some time doing a mock roleplay to test yourself, I would be more than glad to oblige. :) Hope you get out of your rut! <3
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