Here are my thoughts:
"I think that I am very lucky because i have a lot of friends. Among my best friends is Mai. She is 16 years old. We live in the same village . She is my neighbor and we are now classmates, so we have been friends for so long.
Mai is tall and slim. She has long black hair. She has got an oval face with big bright eyes, a high nose, and a small mouth. Mai is very beautiful, especially when she smiles. She is helpful, caring, and honest. When her friends have difficulties, she always tries her best to help them. Although we nearly have the same tastes and interests, we have some different characteristics. I am sociable and enjoy telling jokes. Unlike me, Mai is quite reserved and likes peace and quiet in the library. But there is mutual trust and a perfect sympathy between us, so we are very close friends. Mai is one of the best students in my class but she is always modest. She is also responsible and careful. I like working with her. She tries her best to finish her work. I think as time goes by, our friendship will be deeper and deeper."
Godo job. The main thing I see in your essay is capitalization. Remember that the first letter of a new sentence is always capitalized, as always is "I." Remember that, and you'll do fine.