Because commas cause readers to pause in their reading, you want to use them sparingly. Although logic would suggest that it makes sense to follow coordinating conjunctions with commas, convention does not call for this usage unless the conjunction is followed by an introductory phrase. Thus, it would he inappropriate to write:
- Yet, I think we should go ahead as planned.
When a short phrase follows the conjunction at the beginning of the sentence, however, it is appropriate--although not absolutely necessary--to place a comma after the conjunction:
- Yet, as I mentioned yesterday, I think we should go ahead as planned.