En muchas lenguas se separa una frase subordinada que comienza con la conjunción que (that) por una coma. En inglés no.
We all knew that we were lucky to have won the competition.
Al igual que en español no se separa construcciones con el infinitivo por una coma de la frase principal.
Peter found it not easy to be honest about his accident.
Al igual que en español no se utiliza una coma en frases relativas no restrictivas .
The book that I read last week was not half as interesting as the new one that I am reading now.
The boy who has won the last match is new in this neighbourhood.
En frases condicionales no se coloca una coma, si la frase principal está al principio de la frase. Si la frase principal esta al final de la frase, se puede omitir la coma.
We would have been rich now if you had won the lottery.
If you had won the lottery(,) we would have been rich now.
No se pone una coma en preguntas indirectas .
They just could not tell when the project would be ready.
You asked whether to go to the cinema or to the theatre.
Después de frases adverbiales se puede poner una coma, pero no es obligatorio.
Please make sure to close the doors before you leave.
Before you leave(,) please make sure to close the doors.

* Frases adverbiales son frases que tienen la función de un complemento circunstancial.