I have quite a few small corrections/suggestions but your English is excellent!

"I’m 25 years old and I’m from Valladolid" - in a written letter like this, I would probably use "I am" not "I'm" but "I'm" is not wrong. Similarly with "we're" later on.

"We love order delivery too!" - I think you probably mean "we love to order takeaway [or “takeout” in the US, I believe] too" (?)

“they love as the first day!" - I think you probably mean something like "they love each other as much as they day they got married"

"they looked me out" - "they looked after me"

"Now, I only have my grandmother and I love spend time with her!" - "Now I only have my grandmother and I love to spend time with her"

"fight" - this makes it sound like you learnt how to beat up people, so you probably mean something like "how to compete"

"a phrase I have ever used in my life:" - I'm not sure whether you mean "I had never used in my life (before)" or "a phrase I have used ever since" or even "a phrase that sums up my life"

"so long as I can play with my friends to basketball, tennis or beach sports in summer…" - do you mean "but at least I can play basketball, tennis or beach sports with my friends in the summer"?

"find out what It was earning my own money" - "find out what it would be like to earn money for myself"

"I have five years by tutoring" - "I have been tutoring for five years".

"prepare their exams" - "how to prepare for their exams"

"to speak right words" - "to say the right words"

"Now, I have four children" - that can too easily sound like you are a mother of 4 children. Maybe "Now there are four children I teach:"

"approve all subjects" - "improve in all subjects"

"their friends" - "about their friends"

"and the older they talk about" - "and the older ones talk about"

"I love listen to them" - "I love to listen to them"

I hope your trip goes well - after reading your letter, I think they will be a lucky host family! :-)

Dear Host Family:

Dear host family:
My name is Miriam. I’m 25 years old and I’m from Valladolid, a little city close to Madrid, in Spain. I live with my dad, Jose Luis and my mum, Maria del Mar. We’re a close family and though we  are all are busy, we try to spend time together by  having dinner, watching a movie, taking a walk around the city. We love ordering delivery too!

My parents have a jewelry store. My mum is responsible for serving customers, and my dad is responsible for accounting. They make a good team! They have been married for 30 years but they love each other very much like   as the first day they met!
Another very important part in of my life is my grandparents. I spent a lot of time with them when I was young because my parents worked so and they took care of  looked me out. Now, I only have my grandmother, and I love spending time with her! She taught me how to knit and now I can make scarfs, gloves and wool hats for winter.

In high school, I played handball for 7 years, and I learnedt many things: fighting, friendship, perseverance, discipline, and responsibility. I was lucky to play with the best players in Spain and, we won a European championship! My coach said a phrase I have always ever used in my life: “there are people waiting for something to happen while others dream for something to happens and you work for that something”. I miss playing a team sport, so long as I can but I play basketball, tennis, and beach sports with my friends play with my friends to basketball, tennis or beach sports during the summer.

After I finished high school, I went to college and I studied law. I have always wanted to be a lawyer to defend the rights of others. I finished my career with a good final grade. It was very difficult because I was studying for 8 to 10 hours a day, but I learned that with hard work anything is possible!

While I was in college, I decided to found out a way to earn money by tutoring other students.  what It was earning my own money and started tutoring. I have five years of tutoring experience . My tasks include are to helping children with homework, how to studying methods, helping students prepare for preparing e their exams and teaching them to speak the  right words. I also teach French.

Now, I have four children: Felix, 12, Judith, 7, Andrea, 10 and Jorge 15 years. Jorge is a very special child because he has ADHD. He is a child  who has a with lot of energy but with a smile and a little patience, we managed this year to approve all  of his subjects. For some of them, I’m like an older sister; they tell me what they have done at school, about their friends and the my  older children they talk about the boys and girls they like. I love listening to them and advising them on what to do.