Please correct my writings..

I studied English throughout the school, but I was often criticised by my friends about the written English. After reading, they told that there were grammatical errors and there was no coherence between the sentences. Then I started to read and write about any topic which I come across. I use to take a topic and write something what I perceive. After spending considerable amount of time I still get those errors. I asked this question to many which includes me "Is there a way to overcome?". Until now, I did not get any realistic answer for this. I have a serious doubt whether should I continue this method or should ask any tutor to help me out on my writings.
This is the first time I choose the second option, I don't know how long will this form of writing help me out. I am confident that I will start exercising seriously. I hope this is the first step of my marathon. In the next post, I will write something about a topic.