If you see an -ing word, look out for a comma.
Unless it's a really short sentence, like, "I should be working" an -ing word always comes with a comma. It's not always right by the -ing word, but it's there.
"Alice ran towards the fire, waving her arms in the air."
And, Or, Nor, For, But, So, Yet
- If and is used to separate an element in a series - three or more things - it should have a comma. "We have apples, oranges, and tomatoes." A lot of people skip this comma, but not writing it gives the sentence another meaning. It's the difference between "macaroni and cheese" and "macaroni, and cheese."
- If and is used as a conjunction - to connect two independent clauses - it should have a comma. "They ran down the street, and the firetruck raced the other way."
A parenthetical is a part of a sentence used to clarify or explain.
"Maria's computer, which she mostly uses for writing, ran out of battery."