Since joining Faithwriters, I've been working a lot on showing rather than telling. I think that sometimes, describing a character's thoughts can be necessary in telling a story. (Which should be done very carefully.) However, most of what needs to be conveyed can be done better in showing -- especially in a Writing Challenge entry.
Also, "showing" allows the reader to think for themselves rather have every detail explained to them. It engages them, urging them to fit together pieces of a puzzle by examining the actions and dialogue of the characters. Which makes the story more fun for the writer and the reader.
Sentence structure has always been a pet peeve of mine. In my writing, as I'm proofreading, if I discover that a certain sentence structure has been overused, I try to shake it up a bit.
This is an invaluable lesson! I find that although I somehow made it to Advanced (by God's grace), I need to work on all the topics that you covered as much as anyone.