Speaking in English

In my opinion, speaking in English without any preparation is much more difficult than writing in English. I am sure that it is impossible for me to chat with a native-speaker naturally. As I talk to anyone else in English, I become nervous and get a stammer. In addition, I have a stiff manner out of control. I wish that I could improve this condition and I try my best to relax myself while I speak in English; nevertheless, it doesn’t work at all. The state really bothers me a lot.