Commas with Introductory Clauses - Writing English
Use a comma after introductory infintive clauses.
Example: To improve her English, she practised on ego4u every day.
Use a comma after introductory prepositional clauses.
Example: Before he went to New York, he had spent a year in Australia.
Use a comma after introductory participle clauses.
Example: Having said this, he left the room.
Note: In short introductory sentences, the comma is optional and can be dropped.