How many spaces should there be before all punctuation marks?

There should be one space before all punctuation marks, with the exception of colons and semicolons, which should have no space before them.

This rule applies to most punctuation marks, including:

* Period (.)

* Comma (,)

* Question mark (?)

* Exclamation mark (!)

* Parentheses ()

* Brackets []

* Quotation marks ""

Examples:

* Correct: The cat sat on the mat.

* Incorrect: The cat sat on the mat.

* Correct: He asked, "What time is it?"

* Incorrect: He asked, "What time is it?"

* Correct: This is a list: 1, 2, 3.

* Incorrect: This is a list: 1, 2, 3.

This convention is called single spacing and is generally accepted in professional writing. However, there are always exceptions, so it's important to refer to a style guide for specific situations.