Most people express themselves easily through talking. There is no one single thing is the perfect way. Each person has the ability to express themselves through different ways some by talking and others by writing.
If you feel you cannot express yourself while speaking, then express your thoughts and emotions on to a paper or on your phone. I always had that problem. When you bottle up your emotions, you may give a huge reaction for a simple behavior and it will cause you to be nervous.
Writing helps me to express myself, organize my thoughts and know exactly what are my emotions. so I always love to express myself in writing. I think I think a person needs to understand himself first, his emotions, thoughts and then he can express himself easily with words.