If we are late, they will be angry. * Being late is a real possibility, so you should use the first conditional.

If I were a child, I would play outside. * Second conditional = If + past tense, subject + would/could/might. The second conditional is used for unreal cases.

Don't use THE when talking about things in general.

My sister is being annoying today, but usually she is nice. (We use progressive tenses for actions that are temporary)

I have not eaten anything today.

You don't need commas if "and" is used to indicate addition.

There are twenty-two students. We commonly used there is/are to express existence.

He is not really nice-looking, and yet he has enormous charm. Use a comma before any coordinating conjunction connecting two independent clauses.

It was raining when I got home last night. * Use past progressive for a longer action that was interrupted by a shorter action in the past.

Everyone has seen that movie.

I fell asleep while I was watching TV. *After while use past progressive.

IBGE, the Brazilian Institute of Geography and Statistics, is an important institution. Don't take for granted that your readers know things.

My father thinks I should stop smoking. * In this sentence, the verb think is a state verb. It is generally not used in the progressive (~ing) tense.