Part 3; please read parts 1 and 2 first.

I have been to the National History Museum, I saw beautiful streets like Notting Hill and I visited Covent Garden and Trafalgar Square. I had the opportunity to worked in Knightsbridge where the Harrods Building is located.

"To work" is the infinitive, "worked" is the past tense. You can't mix them.

Once I walked through across Tower Bridge and for almost three weeks I worked as a peddler street vendor in a stall closed to Westminster Bridge.

1/ You walk across a bridge but through a neighbourhood.

2/ Strictly speaking "peddlers" are vendors who go from place to place rather than being at a stall.

I woke up very early and the Underground was always crowed with of people no matter what time was...I left London after six months because I accepted another job in the south Ovest west . Since that time I have never came gone back but I hope I will have another opportunity in the future to be there again.It was such a incredible experience.

1/ Normally you wouldn't capitalise the U in underground but in this case it's the official name of the railway network. Official names are capitalised.

2/ The expression south west on the other hand is just a description of an area, and is not capitalised.

3/ Come = venire, go / gone = andare. When you are next in London you will be able to say "I have come back" but as long as you are away from it you say "I hope to go back".

Your language skills are very good.

London

Part 2; please read part 1 first.

My roommates were from different backgrounds and nationality nationalities, the relation was normal, I was not able to talk and understand almost nothing.

1/ If they were from "different" backgrounds then there had to be more than one. You therefore use the plurals "backgrounds" and "nationalities".

2/ Sorry, but I can't figure out what you're trying to say with "the relation was normal".

3/ In the last clause you're falling into one of the key differences between English and Italian. Italian uses a form that English considers to be incorrect; the "double negative". For example, in Italian you might say: "Non ho capito niente". In English this literally translates as "I have not understood nothing". You can't not understand nothing; instead you do not understand anything. So what I believe you are trying to say there is: I was not able to say or understand almost anything. (Also you would not use "talk" in a sentence like that; talking is the action that you perform when you are saying something. )

Everything was expensive and I was washing my clothes and hanging them in my room in order to save money.

If you use the gerund form for one word (washing), you should use it for the other (hanging). An alternative form is "I would wash my clothes and hang them in my room"

I worked in a big chain of restaurants for over four months. The salary was not bad but I had no time for studying English.

In this case you could also say "to study English".

In spite i had just one day off i could visited enough this incredible city.

I'm not completely sure what you're saying there but I think you mean that you had just one day off per week, and that you couldn't get enough of the city. In other words, you were never satisfied that you had seen enough and wanted to see more. You can't use "in spite" by itself there, because that means that you are defying something, and you haven't said what that is. So what you could write is:

In spite of me having only one day off per week, I couldn't see enough of this incredible city.

During the night the Big Bang Ben was beautiful and the London Eye too.

I think you mean "Big Ben"; the Big Bang was the explosion that started the universe. Also technically Big Ben refers to the bell in the tower, but a lot of people call the tower, clock and bell "Big Ben".

And I'm out of space again.

Part 1 of 3.

London

1/ The pronoun "I" is always capitalised in English, unlike io in Italian.

2/ The fact that you're in the same village is separate from the fact that you have been living in the same house for 20 years. You therefore need "and" to join those two thoughts.

3/ You need "the" to determine which village you're talking about . Just saying "same" is like saying "stesso" instead of "lo stesso".

4/ Having read the rest of this I think you meant "I HAD been living... etc"; that is, you had been at the time that you moved to London, not that you are now.

When I decided to quit my job and fly to London this was one of the reasons. I wanted some new motivation, I was bored and a little upset about everything.

1/ If you say "one of the", then there has to be more than one reason. Reason therefore needs to be "reasons", in the plural.

2/ "Some" is a suggestion; it's just as more common way of saying it.

Well, at the beginning i couldn’t imagine to do doing it because of course of the language issue, not to mention how difficult it was to find a job there.

1/ It would take a couple of pages to explain when you use the infinitive ("to something") and when you use the gerund (the ing ending), but it will come more easily with practice.

2/ Of course isn't really wrong, but it doesn't seem necessary here.

3/ It's not the language as such, but the issue of you not being familiar with it.

4/ You can't say "how difficult was" because it doesn't say what was. In this case you use the pronoun "it".

5/ The lack of "a" in front of "job" is the same issue as the lack of "the" before "same".

I have had found one hostel first in Northfield and after few months I moved closer to the city center, at Earl’s Court.

1/ "Have" is for the present tense (ho), "had" is for the past tense (avuto").

2/ First is probably redundant here.

3/ Note that "center" is an American spelling. International English (including England) uses centre.

I'm out of space.