Here is a correction --  I hope that it helps!  You have several small mistakes, but it is easy to understand your text -- and that is important!

I am learning English

Hello.

I want to tell you about my day.  Today is August 17th.  

I got up at 10:00. My mum prepared my breakfast.  My brother played computer games and my father was already at work.

I washed and ate. Then I studied and played the guitar. I went for a walk with my best friend. I love my friend very much.

In the evening, I went home. My family and I had dinner.

Then I watched TV and went to bed.

I learn English

Hello.
I wont tell about my day.Today is 17 Augustus.
I stand-up at 10:00 o‘clock.My mum prepared my breakfast.My brother played computer gemes and my father was already at work.
I washed and eaten.Then a studied play the guitar.I went to walk with my best friend.I love my friend very much.
In the evening a went a home.My family and me had dinner.
Then l watch tv and I went to bed.

First dialog

- Hi.
- Hello. How are you?
- I'm fine. And you?
- Not bad?
- What is your name? My name is Marat. Where arE you from?
- I AM from England. I live in London. Where are you from?
- I AM from Russia. I live in Izhevsk. It is A small city IN THE middle of Russia.
- WHAT DO YOU DO?
- I am a software developer. I work in A small company in Izhevsk. Our company
works with A US company. I want to improve my English.
- Good luck WITH your learning.
- Thank you. See you later.

Suggested correction.  Hope that it helps!

Resolutions

I am going to practice English everyday, not only just a few days at a week. I will be read English books and I want to find friends to for speaking practice. And, of course, I will pay attention not only to the mistakes that I make but also to my achievements, as it will help me to feel happier within better about learning and to have more fun.
I will be often communicate with my friends often, even if they so live far away and give a will send them small, pretty presents or sent a postcard. Also I also want to find new close people and like-minded persons people nearby.

Hello, everyone!  My name is Aliaksei.  I want to learn English, because I would like to live in the US or Canada in the future.  I am 26 years old, married, and have two children.  I am a network engineer at a large corporation that manufactures/designs metal roofs.

Only a few minor corrections necessary in the first sentence!

A Tidal Breath (2)

Stephen stepped up to his son and laid A hand upon his shoulder; it was AS fragile as a bird's bones.
“It’s them,” the boy said.
“Yes.”
“How much time do they need to finish a job?”
“Six days. They have a strict project deadline. We should go now—”
“Where?”
“Fowling. Remember?”
Johnnie shook his head.
“What about them?” he asked. “I’d like to see how they do their work.”
“Sure. A little later—“

Suggested corrections, hope that it helps!

I don't like winter

I was born on January 13th. Some people says that if you was were born in the summer, that you will might love summer; if you was were born in the winter, that you'll automatically love winter automatically. So, I think that my parents lied to me and that I wasn't born not on in January. I think that I was born in July :)

Rather than correcting the mistakes, I thought you might find it more useful if I pointed out which ones need a bit more work.  Hope that it helps!!

In terms of prepositions, the mistakes are in the following sentences:

6

12

16

25

32

36

42

46

Then there are a few others that are incorrect, though not because of the prepositions:

5

20

29

30

31

48

50

48

(Suggested correction, hope that it helps!)

I am a native Russian speaker. of Russian

Hello. My name is Mary. I am a native Russian speaker. I can help you for sruding to study Russian. Our lessons will would be in on Skype.
See you soon, my friend!