Comma Rule Number 2
A comma is necessary to separate a long introductory element before a main clause. Rule 2 holds true for both simple and complex constructions:
Even though ignorant of our culture, we must always be kind to strangers. (Simple)
Since Constance is new to our company, all of us should strive to help her. (Complex)
It’s always correct to set off any introductory element with a comma, but a more modern lean toward fewer commas in novels has made the practice optional for shorter elements. Either is acceptable:
Later, you can join us for dessert. Later you can join us for dessert.
Comma Rule Number 3
Commas separate items in a series:
James found blondes attractive, redheads adorable, and brunettes irresistible.
The final comma before the conjunction is always correct. However, the journalistic practice to omit the serial (or Oxford) comma is every author’s option:
James found blondes attractive, redheads adorable and brunettes irresistible.
Also correct is an occasional asyndeton (a-SIN-dih-tawn), the intentional omission of the normally occurring conjunction (and, or, but, for, nor, so, yet) in a series of words, phrases, or clauses:
James found blondes attractive, redheads adorable, brunettes irresistible.