Punctuation

Commas, colons, dashes and apostrophes each have a few jobs. The test rewards using them only for those jobs, and leaving them out everywhere else.

How to do it

Extra information that could be lifted out of the sentence is set off on both sides, by two commas, two dashes or two parentheses, never a mix.
A colon comes after a complete sentence and introduces a list, an explanation or a quotation.
Do not put a comma between a subject and its verb, between a verb and its object, or before a prepositional phrase that finishes the thought.
Apostrophes show possession (the captain's log, the sailors' pay) or a missing letter. They never make a plural.

Example

Wrong The prize offered by Parliament, was worth a fortune.

Right The prize offered by Parliament was worth a fortune.

"The prize offered by Parliament" is the subject; "was" is its verb. Nothing separates them.

Traps

If you open with a dash, you must close with a dash. A dash opened and a comma closed is wrong.
When in doubt, the choice with fewer commas is right more often than the one with more. Each comma needs a reason.

Practice it

Every practice question comes with a full explanation, including why each wrong choice is wrong. Free, with no account.