1) We can use "before" and "after" to talk about when something happened:

After finishing school, John when on to study at University.
Before crossing the road, always look left and right for cars.

** Note that the subject (ie who is doing) of the ING, is the same as the second part of the sentence. - John is "finishing"

2) We can use "by" to explain how something happened:

He passed his exams by studying really hard.

* if the ING clause comes first, we use a comma.
** if the ING clause comes second, we do not use a comma.

3) Without + ING 

Can you play the piano without looking
Without checking the text book for help, answer the questions. 
He ran a whole marathon without stopping to walk.
I worked all last night without taking a break.

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Try exercise 4, p. 125, Unit 30 (Business Grammar Practice)