Julia Said:

how i can improve writing skill though i have no teacher except internet?

We Answered:

Internet, you say? Internet can always be your teacher, my friend.

Keys to improve writing-
-grammar (they're, their, there) all that stuff
-write a lot
-read (this is the most important)
-use thesauruses, and dictionaries. (know you're homophones, antonyms, etc,) most of these you can search online. (e.g. blasphemy definition)
-friends (have a friend who knows English well, and let them help you become a fluent English speaker)
-talk in the language everyday (as much as you can)
-type on your computer a lot. Whenever you spell something wrong, your computer will underline the wrong word with red. right click the word to see the correct spelling
-while watching TV, put on subtitles to read.

http://grammar.ccc.commnet.edu/grammar/ (for grammar)

Writing-
Try at least everyday to write for 15 minutes straight. no breaks in between. Just write about anything. Just write, write, write, until the time's up. Even if you can't think of anything any more, still write about SOMETHING.

Reading-
For you age, I would suggest to read every night for at least 30 minutes. (More if you can) If you have a break from work, read. Read like mad! (You can even read online for free, it's called fanfiction.net
fictionpress.com
These ones are legal, and have been made by real people who have put their work on these sites)
Also, while reading, whenever you see a word you can't comprehend b your current knowledge, always check the dictionary, write it out 10 times, and remember how it is used in a sentence. That helps build your vocabulary.
NEVER read any books that are easy. Try aiming for reading books with words you can't quite understand, though don't pick out a book too hard, or you won't enjoy reading it.

Website for becoming a better writer-
http://www.positivepath.net/ideasMA21.as…
http://www.efuse.com/Design/wa-more_bett…