Place comma after So?

Give us an example !
My crystal ball is foggy today.

Only when used in informal speech:
So, what do you think?
So, that's it for today's class.
So, let's see. What do we have here?
So, tell me about yourself.

Thanks Mentee. However, is this British usage?

This is both American and British usage.

You are welcome Mainak. Thank you John for answering.
Its usage is somewhat similar to 'well'.
Well, what do you think?

Absolutely.
"Well" is equally acceptable. It's a matter of style, and all you have to do is choose one and be consistent.

Thanks John for your valuable comments!

So, indulge in reading