Conventions are the mechanics of writing, the capital letters, the punctuation. They are correct grammar and spelling. They are knowing when to start a new paragraph because you are introducing a new idea.
Make sure you capitalize the first letter in each sentence and nothing else except proper nouns (the names of people, places, and things).
Make sure each sentence ends with a punctuation mark and that you don’t just run multiple sentences together without a break.
Add a comma after an introductory part of a sentence, and add one before a conjunction, like I just did. I also just added a comma to separate off unnecessary information.
Make sure to keep using the same verb tense. Don’t start using present tense and then change to using past.
Here are some proofreading marks that you can use on your papers when you edit them.
¶ new paragraph
^ insert something
(deletion symbol from Wikimedia)