1. Coordinate adjectives are the adjectives which are placed in sequence with another adjective to describe or to modify a noun. Hence, commas are used to separate two or more coordinate adjectives.
2. When combining two independent clauses, a comma must be placed before the conjunction.
Independent clauses refer to the groups of words which can stand independently and create a meaning. An independent clause has a subject and verb.
For example, I went to the market, but forgot to take money.
In the above independent clause comma is placed before the conjunction 'but'.
3. A comma should not be used to separate compound elements.
Commas are frequently used punctuation in a sentence, hence they are used to create a short pause in a sentence.
Hyphens are used to show a compound sentence and not commas.
