1. I have never seen her before.
2. They haven't come yet.
3. We haven't seen them since (с тех пор как) they went to Canada.
4. This is the third cup of lea I have had.
5. I have known them for 3 years.
6. They haven't studied of late.
7. Yesterday they had come home by 7 o'clock.
8. When I came home my children had fallen asleep.
9. When I arrive in Tomsk it will have been night.
10. By the evening tomorrow the conference will have finished.
Remember:
already - only in affirmative sentences (уже)
yet - in negative sentences (ещё не), in questions (уже)