PUNCTUATION TIPS - THE APPROPRIATE USE OF COMMA.

A comma [,].

Is used or to:

Separate words in a list, but you must sometimes omit them before "and."

Example - I bought a red, pink, and white roses tea, coffee, milk or hot chocolate.

Separate phrases or clauses.

Example - If you keep calm, take your time, concentrate and think ahead, then you're likely to pass your   test.

Before and after a clause or phrase that gives additional, but not essential, information about the noun it follows.

Example - Princely Okwuego, who is very popular with writing articles, leaves in Nigeria, but originated from United Kingdom.

Do not use comma before and after a clause that defines the noun it follows.

Separate main clauses, especially long ones, linked by a conjunction such as: and, as, but, for, or.

Example - We had been looking forward to our holiday all year, but unfortunately it rained every day.

Separate an introductory word or phrase, or an adverb or adverbial phrase that applied to the whole sentence, from the rest of the sentence.

Example - Oh, so that's where it was. As it happens, however, I never saw her again. By the way, did you hear about Princely's car?

separate a tag question from the rest of the sentence.

Example - It's quite expensive, isn't it? You live in Nigeria, right?

Before or after 'he said', etc. When writing down conversation.

Example - 'Come back soon,' she said.

Before a short quotation.

Example - Princely said, 'little things affect little minds'.

[Oxford Advanced Learner's Dictionary, New special Edition, 6th.]