Commas with Adverbs

Use a comma after certain adverbs: however, in fact, therefore, nevertheless, moreover, furthermore, still, instead, too (meaning 'also').

Example: Therefore, he didn't say a word.

If these adverbs appear in the middle of a sentence, they are enclosed in commas.

Example: The thief, however, was very clever.

The comma is optional for the following adverbs: then, so, yet.

Example:

 So, she entered the house.

 So she entered the house.