Corrections in red.  Stylistics in blue.

Using "if"

First conditional
• If I go to the school, I will learn many things.
• If I read the book, I will know the end of the story.
• If I get up early, I will see the sunrise.
• If you try to cook, we will eat tonight.
• If you study English, you will speak with many people around the word.

Second conditional
• If you were a fly, You could listen those guy over there.
• If she were the President of the United States, I couldn’t come back.
• If my sister realized her dreams, she would be the happiest woman in the world. 
• if she sang better, her friends wouldn’t run away. (It is impossible for her to sing well.)
• If you were an alien, you could understand your girl friend.

Third conditional
• If you had pardoned (better:  If you had forgiven) your friend, you would have been happier than you are now.
• If she had studied more, she could have been a good teacher.
• If he had built a big house, he wouldn’t have moved to another apartment.
• If I had still had played the guitar with my band, I would have been a famous musician.
• If my friends had bought a boat, we could have gone to the Sardinia.