how to improve my grammar

i always doubt if the essays i have written have mistakes that not even my school teacher could have pointed it out.Every time i am asked to write essays and that i was so caustious so as not to make a single mistake.At all time my essays were returned i was so disappointed to see so many lines of which it is known as "incomprehensible" to the sentences.I admit that my english is really miserable to be understood.Incidentally,i would like to consult a teacher online so that i can obtain more useful instructions than my school teacher's line

P.S. Perhaps the message above has some mistakes,i hope u will indicate me with the message return.

The method that works best for me when learning a new language is reading in that language. Read, read, read as many books in English as you can. Of course, an online tutor should help quite a bit as well.

And concerning the grammar in your message; it isn't that bad. The two main things I would change are: When the letter "I" is referring to one's self, it should be capitalized. You should also leave a space after you put a period.

Example:
-[this is wrong] Here is a sentence.Here is another sentence.
-[this is correct] Here is a sentence. Here is another sentence.

I hope that helped. If not, let me know. :-)