Reduced Adverb Clauses : An Adverb Clause can be reduced only when the subject of the Adverb Clause and the subject of the Main Clause are the same :

1-  Omit the Subject of the clause and the " BE " form of the verb :

While I was watching TV , I fell asleep.

While watching TV , I fell asleep.

 

2-  If there is no " BE " , omit the subject and change the verb to " -ing " form :

After I signed the report , I gave it to the director.

After signing the report , I gave it to the director.

 

NOTE :

While the teacher was speaking, I fell asleep. ( cannot be reduced, because the subjects are  different )

 

A :  Reducing Adverbial Clauses of Time :

1 -  Two actions happening at the same time :

      Janet was sitting in an armchair and reading a book.

      Janet was sitting in an armchair reading a book.

2 -  One action happens during another action :

      David was watching TV while she fell asleep.

      David fell asleep watching TV.

3 -  One action happens before another action :

      After they found a hotel, they looked for a restaurant.

      Having found a hotel , they looked for a restaurant.

 

B -  Reducing Adverbial Clauses of Reason :

1 -  The sentences answering " WHY " questions :

      Since she felt sick, she went to bed early.

      Feeling sick, she went to bed early.

2 -  Negative :

      I didn't know his address, so I couldn't contact him.

      Not knowing his address, I couldn't contact him.

3 - Negative , ( one action happens before another action ) :

     I had not understand what he said, so I asked him to repeat the directions.

     Not having understood what he said , I asked him to repeat the directions.