Punctuation is important because those little marks are like signs along a roadway, helping your reader navigate your document. When you put punctuation in the wrong place, it can change the intended meaning of your sentence and send your reader in the wrong direction.

Here are three common punctuation problems.

1) Putting a Comma Before 'and' in a Series (or Omitting the Comma)

The company makes pocket calculators, electronic keypads, and pocket translators.
The company makes pocket calculators, electronic keypads and pocket translators.

Which is correct? Both are. Whether you use the serial comma is entirely up to you. The key is to be consistent. Make a decision and stick to it throughout your document. Inconsistency is the grammar mistake.

2) Using Two Spaces after a Period or Colon

The two-space rule is a hold-over from the days when printing presses and typewriters used letters that were all the same width. Today, computers compensate for the varying widths of letters and only one space after end punctuation is the preference.

3) Putting a Comma Between the Subject and the Verb

incorrect I suggest that Billy, Pete and Mary, attend the conference.
In this sentence, a comma splits the clause's subject Billy, Peter and Mary, from the verb attend.
tick1 I suggest that Billy, Peter and Mary attend the conference.
A comma after Peter would also be OK in the above sentence.