Ответ:
1. He will feel better as soon as he doesn't eat trash food.
2. If she works hard, she will earn some money for the journey to the seaside.
3. He would write better if he read more books.
4. If you wear this jacket today, you will be cold.
5. If she knows the secret, she will never tell anyone.
6. They will help me if it is necessary.
7. Don't open the door if someone rings the doorbell. (imperative conditional)
8. If she had English practice abroad, she would speak better.
9. We would catch the last bus if we left at once.
10. If you go on a diet, you will lose weight.