With very few exceptions, commas should not be inserted between the subject of a sentence and the verb.
A comma indicates a break in the sentence, and since the subject is linked to the verb (the subject carries out the action expressed in the verb), it is incorrect to separate the two by using a comma.
Writers may be inclined to insert a comma in speech because the speaker may pause at this point in the conversation. With regard to narrative, however, the insertion of a comma between the subject and the verb separates the direct link between them. This makes for awkward reading as the reader has to understand the reason for the break, and if there is one, it can spoil the flow of the sentence and then the enjoyment of what is being read.
Just to put all of this in perspective, recently, I had to proofread a novel that had already been copy-edited by one of the largest publishing companies in the world. The copy-editor persisted in placing commas between the subject and the verb.
Here are just a few examples of what I found:
Doris stood in the doorway between the kitchen and the hall, and sighed.
The pain was slowly making its way up his jawline, and was now pounding like a pneumatic drill in his temples.
She didn’t argue this time, but slipped outside the workshop and spoke with the two men waiting outside.
He felt so guilty, and vowed never to abandon his brother again.
He glared at her, but didn’t speak.
Suffice to say that in none of the above examples should the comma appear.