English's problem

I always make a lot of mistakes in my essay :(
I always tried my best when I was writing. However I always make a lot of mistakes..
Today, I did work-shopping with my partners. I wrote argument about gay marriage. I think they were like my essay. But, when they read "...some people are born with gay blood..." they laughed at me. At first, I did not know why did they laughed, but after that I discovered they laughed at me just because my words "gay blood". They said they had never heard that before. Actually, I had never heard, too, but I did not think its are very strange that people can laugh a lot when they read it. Maybe the way we write in my country is very different with the way American writing. I think I have to study more...
I do not know how to improve my English???
This is always a big question for me, and I have to find out the answer...
Hope I can answer my question some day :)


Hopefully !!!!!