Most of the time I have felt that I cannot stick to my subject and divert into several intricacies finally losing track of the my main subject? Is there any way I can avoid this?
well I think maybe spending sometime and trying to figure out what causes you to go off track in the first place. Maybe spending more time planning the story out, either on paper or in your hear? It really depends WHY it happens.
Maybe the fact your a going off subject is a good thing, maybe thats what is gonna turn the novel (I assume its a novel) into what its gonna be. Tom Keep on writing, never put down the pen.
Problem definition is often a big step toward solution. You know you're going off topic. Another topic pushes into your consciousness. You might want to decide whether the original topic was as worthwhile as the new one. Or, you might want to include the new topic as a component of the original. I was writing "Anacapa" (see on this thread). I needed to write about this guy, who looks alot like myself, meditating on a beach and sitting quietly and taking stock of his life. Grey whales came to mind, so I put a family of them into the story, but I never succeeded in linking the whale story to the meditating guy story. At this point I knew that I didn't have anything worth reading. So I decided to add something to grip the reader, something original, something that had never been tried before, like 'boy meets girl'. Suddenly the island this guy was sitting on had a lighthouse, and the lighthouse had a Forest Service officer to look after it, who happened to resemble a beautiful blonde actress, Deborah Unger. Of course, this beautiful blonde Forest Service officer was lonely and frustrated. They had to meet. The story went on from there. The whale family came and went from a distance, and a strict reviewer would say that the whales added nothing to my little short romance. However, most of the readers who commented, liked it, and it was a good exercise for me as a new writer.