Here are a few suggested changes:

Presentation

Hi, I´m Manuel from Spain. I was born in Valencia, an incredible city on the Mediterranean coast. The sunlight, the traditional Paella Valenciana and its friendly people are appreciated by visitors from many countries. Actually, I´m living in Switzerland, and I would like to meet native English speakers. and i offer my Spanish native speak and do my best.[I am a native speaker of and Spanish and will do my best to help you.]  I´m iterested in many themes like tecnology, sports like kitesurfing and meeting personspeople withfrom other cultures. Greetings.

You use "a" before a word that starts with a consonant (a dog) but "an" before a word that starts with a vowel (an apple).  We generally say "on" an island or "on" a coast but "in" a county, state or city.  I changed "persons" to "people" because that sounds more natural and added some punctuation changes (commas are even hard for native speakers of English!).  Nicely done, though.

At – For a precise time, for indicate a place
On – For days and dates, surface, a part of the body

In – For months, years, centuries and long periods, enclosed space

Let's take a look at the examples using the prepositions: On, At and In. 
On
For days and date:
My family will arrive on Friday. 
He was born on the 20th day of January in 1983. 
I'll be there on Christmas Day.
For a surface: 
They're putting their name on the wall. 
The notebook is on the table. 
Let's lie down on the floor.
For a part of the body: 
He kissed me on my forehead. 
She's wearing a pretty ring on her finger. 
You can put your hand on my shoulder. 
At
For a precise time: 
We will meet you at 3 p.m. 
The limousine will stop here at 7:35 a.m. 
I want you here at dinnertime. 
Used to indicate a place: 
It's at the corner of Redmond Avenue with Freedon Street. 
There is a kids party at the mall today. 
There are a thousand people at the club. 
In
For months, years, centuries and long periods:
I love read newspapers in the morning. 
We have a long holiday in the summer
The new season will start in July. 
For enclosed space: 
I'll wait for you in the garden. 
Let's meet in France. 
He looked me in the eyes.

I found it one site, its interesting. Have a great afternoon