arrow Clauses are incredibly useful. There are independent clauses, dependent clauses, and adjective clauses. For now, we'll focus on identifying the independent clause. An independent clause can function as a sentence on its own. Ex: The dog ran away.
arrow We can throw a dependent clause on the independent clause. Keep in mind that a dependent clause cannot function on its own without the independent clause. Ex: Because there was a loud noise,the dog ran away.
I'm not going to go into everything grammar, and I'm sure you're wondering how exactly this helps you. If you can identify the parts of the sentence, it's easier to make it flow. A good, solid understanding of grammar will help you to succeed in your writing. Try to keep sentences from sounding choppy, but don't allow for a run-on. Like user Pikachu has Fainted suggested, say it before you write it.
The best way to improve is to learn how to take criticism. You are not your work, and your work isn't you. If someone takes the time to point problems with something you've wrote, resist the urge to "defend" yourself.
Instead, take notes. Ask questions, and understand where they're coming from. If you think they're trolling you, then don't start any forum drama, and don't respond to their posts.
Other than that, yeah. Like Saffron and Pikachu have said, it's really just a matter of knowing how things are supposed to fit together, and what does and does not sound weird.
For a long-term solution, read more. Sentence structure can vary depending on the subject matter and the desired effect. The best way to learn the difference is to find examples that feel right to you when you read them, and compare them to ones that don't.