Dear friend,
The good news is, you can overcome this....but you must put your mind to it and be willing to stick your neck out a few times. Is this something you face at work alone, or even with your friends?
Some of the reasons are-
1. you lack confidence, or have poor self esteem
2. you are not fluent in English
3. you are not well-read enough to contribute to a discussion
I have met several people who have problem 2 or 3 and yet still speak well, primarily because they are so confident.
My advice is,
identify the root cause of your problem... do you lack confidence or self esteem? One way to figure it out is to see your behavior with different kinds of people. Are you more confident speaking to your friends than to colleagues? Why? Are you capable of speaking better with people you believe (sometimes unconsciously) are inferior to you?
If this is the case, then you cannot speak when you believe the other person is superior to you. Remember, superiority/inferiority here is just your perception, it's what you believe. It is not fact.
Self esteem and self confidence can both be worked upon. If you are interested, i'll send some resources.
If the problem lies in your English language skills, then start working on your English speaking skills.
Some immediate steps you can take is----
1. Increase your awareness of issues, events, etc. by reading the paper, mags, journals, forums. think about everything and take effort to form your opinions on matters in advance. For office situations, write your ideas down on paper, so that it'll be easier for you to recall and say them in a meeting or official discussion.
2. Start sharing these opinions, first with people you are more comfortable with and later with colleagues, and groups of people.
3. If you can recall a conversation where you couldn't speak, work on it. write down the conversation, and see where all you could have spoken (but didn't)...analyse why you didn't say anything. what were your thoughts, how were you feeling...did you agree with the other speaker or disagree. were you scared to contradict? Analyse, and think of all your possible responses, and practice by saying them out loud. Try as much as possible to understand your limitations.
4. Practice speaking to a mirror or in an imagined conversation in the privacy of your home
5. Keep a victory log to record every time you did speak the way you wanted. try to remember how you felt then, were you very confident or happy?
6. Be alert to feedback.
7. Observe those people who you think communicate well. is there anything you can emulate? (not parrot) and finally
8. It doesn't matter if you make a fool out of yourself. if people put you down when you try to speak up, or if you feel embarrassed or foolish. you have to keep trying, and keep improving. if you need anymore resources on dialogues, etc.,
Do get in touch with, I'll send as many resources as I can. There are excellent self-help books on these topics. Believe it or not....they do work!!!!! So just keep up the chin and don;t get too worried. Just work hard at it!!!!!
PS: btw- Listening is also a fantastic skill, but you must listen with confidence not with the nagging worry of not being able to speak.