When you DO use a comma after "often":
* When "often" is used as an introductory word:
* Example: "Often, I go for walks in the park."
* When "often" is used as an interrupter:
* Example: "I go for walks in the park, often with my dog."
When you DON'T use a comma after "often":
* When "often" is part of the main clause:
* Example: "I often go for walks in the park."
In summary:
* Use a comma after "often" if it acts as an introductory word or an interrupter.
* Don't use a comma if "often" is part of the main clause.
Let me know if you have any other grammar questions!