1 - Use "quickly" instead of "short." Even if a sentence is grammatically correct, it still might be unclear or hard to follow. Awkward phrasing or unnecessary words force your reader to work harder to understand what you mean. Very long or over-complicated sentences can lead to the same problem. Cutting extra words, tightening up awkward phrasing, and making sure your sentence isn’t too long are good ways to make your writing clearer.

1 - A possessive pronoun may sound redundant or awkward when it’s already clear from context who an item or idea belongs to. In these cases, it is often more idiomatic to use a determiner instead of a possessive pronoun.
Possessive pronouns are a better choice when context does not make it clear who an item or idea belongs to.
2 - Prepositions are function words that indicate how a noun or noun phrase relates to the rest of the sentence. Some prepositions, such as in, on, after, or since, express temporal or spatial relationships. In other cases, the relationship is more abstract and the best preposition to use may depend on the words around it. These are known as “dependent prepositions,” and they do not follow any clear pattern.
Choose prepositions carefully because sometimes changing a preposition can completely change the meaning of the phrase. A good dictionary will provide guidance on which prepositions to use with which words.

1 - This is redundant.
2 - Spelling the numbers is recommended.
3 - This is the correct way to construct this part of the sentence.
4,6 - Use this instead of "so."
5 - Add this to complete the sentence.

1 - An introductory word (Unfortunately), phrase (Before the party), or clause (If you can join us) sets the stage for the sentence. Introductory clauses and long phrases must always be followed by a comma, while single words and short phrases may or may not. Use a comma when the phrase is a verbal phrase (Running away), a non-essential appositive, or an absolute phrase (The audience waiting). Also use a comma when a pause is necessary or the lack of a comma will cause confusion.
2 - A comma symbolizes a slight pause that can separate ideas or grammatical structures in a sentence. There are dozens of ways to use commas. Some common cases include separating parallel adjectives, setting off nonrestrictive phrases, separating items in a list, and separating an introductory phrase from the rest of a sentence.
3 - A pronoun is a word that is used as a substitute for another noun or noun phrase. They come in a few different forms depending on what they refer to and how they’re used in a sentence.
Subject pronouns include I, you, he, she, it, we, and they. Object pronouns include me, you, him, her, it, us, and them. Possessive pronouns include my, your, his, her, its, our, and their.
4 - Most nouns have a singular and plural form. Words like one, many, or these can affect whether you use the singular or plural form. For example, it’s correct to say one person (person is the singular form). But if you’re talking about more than one person, you’ll need to say many people (people is the plural form).
In some cases, you’ll need to substitute a different word to make everything agree. It’s correct to say a lot of ideas or many ideas. But you can’t say many creativity; you’ll need to say a lot of creativity instead.

1 - An introductory word (Unfortunately), phrase (Before the party), or clause (If you can join us) sets the stage for the sentence. Introductory clauses and long phrases must always be followed by a comma, while single words and short phrases may or may not. Use a comma when the phrase is a verbal phrase (Running away), a non-essential appositive, or an absolute phrase (The audience waiting). Also use a comma when a pause is necessary or the lack of a comma will cause confusion.
2 - Some writers insert commas anytime they would pause slightly in speech, even if the comma isn’t required by any rules of punctuation. Sometimes this is a good way to achieve a casual, speech-like effect in your writing, but the technique should be used sparingly. Using too many unnecessary commas can make your writing stilted and choppy.