Writers block + Sentence structuring

My personal secret for this is to view my story as its own world, not as something I'm writing.

I don't only think of what the readers want to see next or try and come up with things I want to happen. I look at what I've set up, the characters, situation, the elements at play, and I try to logically conclude the course of events.

If you can't figure out what 'B' is in A-->C, then just take a closer look at what's in A and think of how it would progress, that progression will naturally create a B, and if that B made from logic rather than pre-determined plot doesn't match your goal for C, then either try again, or change C to match the logic of your story.

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Sentence Structuring-

When writing in third person, I tend to describe what the character is doing or who's speaking, and then put in their dialogue. If I've done too much of that, I'll do their dialogue, and then describe what they're doing or who's speaking afterward.

Kane spoke up worriedly, "That's pretty dangerous!"

"You'll just have to deal with it till I think of something better," Sun grimaced.

Kane laughed, "We both know you can't do that."

You can also ignore describing character actions or who's speaking so long as the person speaking is obvious. This can be used to improve flow in conversations with a lot of back and forth. You can also describe a character's actions, thoughts, etc, and then do their dialogue in a separate line just after.

Kane listened closely for any sounds of life, a solemn look spread across his face.

"She isn't breathing..."

This can be used to create tension or drama (thanks to the spacing between the actions and the single line of dialogue), or can just mix up your writing!

All of this can apply to first-person as well, just make sure to use the appropriate first-person wording and use 'I' instead of the protagonist's name during their dialogue or descriptive segments.

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I don't have any concrete way of describing my sentence structuring, all I can recommend doing is including my previous suggestions into your writing (such as less repetitive wording, more synonym usage, unique words, etc).

Read the works of other big writers (preferably not web novel writers), take note of how they craft their sentences, how their writing flows together, determine a style you like and gradually shape it around your preferences.

Clean up your own writing bit by bit as you use it. Make sure to revisit your old works from time to time and read them with fresh eyes, note anything that seems clunky and compare them to your newer works to see if you still have similar problems in your writing.