Watch out! The use of Present Perfect / Past Perfect

We don´t use Present Perfect when an exact past time is mentioned and there is no connection with the present:

X - We´ve been to London in 1997.

CORRECT - We went to London in 1997.

. But we can use the Present Perfect if the period mentioned includes the past and present:

- We´ve been here since six o´clock.

- I haven´t done much work today.

- It´s been raining for ages.

. We use Past Perfect for something that happened before something else. We can only use it with another Past tense:

- I went to see hiem because his wife had asked me to.

. We omit will in time clauses:

X - I´ll phone you as soon as we will have arrived.

CORRECT: I´ll phone you as soon as we have arrived.