communication skill

In my opinion it is better not to think of grammer while we speaking,but to be able to speak fluently you should have some knowlegde of grammer unless the langauge is your mother tongue. With our mother tongue grammer is automatically presented. To improve your communication skill, try to have a chat with your friends once in a while and discuss some of the topics which you guys are interested

Yes, you should know the rules first. I'm not saying that you memorize them. Just know them by heart. In learning whatever language, try to read books or watch movies in that language. Eventually, without even memorizing the rules, you'll get to develop the instinct that "if it doesn't sound right, it is definitely grammatically wrong."