Jesus,
You did a good job with the letter. I thought there was an overuse of the word "so" to connect ideas. Here is a modified version of what you wrote for your consideration. See what you think.
Tony
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Dear Ms Evans,
I am responding to your advertisement in the Tourist Information Office and would like to apply for the position of tourist guide.
I have been studying English for many years and have gained the appropriate skills to communicate fluently in that language.
Furthermore, I have had previous experience in this kind of work, and I also have a good knowledge of dealing with people.
Naturally I know my city very well because I have lived here all my life. As a result, I am thorouhly familar with the most important monuments and sights which tourists would like to visit.
Overall I am certain that I would do an excellent job for your agency, and I am enclosing a copy of my curriculum vitae for your consideration.
I look forward to hearing from you.
Yours sincerely,
Jorge Martin.