Writers and editors vary in their use of punctuation. Some prefer heavy or formal punctuation, lots of commas and a few semicolons and colons. Others tend to be more restrained, using punctuation marks more by rule than sound. You have flexibility, but it is best to show come consistency.

The Comma:

Example: The leader of the project was reluctant to change the schedule, but he did so at the insistence of his superiors.

But. Do not use a comma when the second clause does not have a subject.

Example, He fell from the balcony and hurt himself badly.

Example: If the expedition had come upon the signs earlier, it would have stopped for the night.

Example: The team worked on running, blocking(,) and tackling.

Example: I came, I saw, I conquered.

Often when the clauses are long, a semicolon is expected.

Example: They arrived at Mandalay, his childhood home.

Example: The old chief sat impassively, thoughtfully, giving no indication he was about to rise.