Hi Sheetal,
It is good to know from your post, that you are willing to improve on your weaknesses. Yes, do not lose heart by adverse comments of what people say, rather start accepting constructive criticism to become more assertive and have a definitive direction in pursuit of your goals.
One important thing you need to note, that many people are nervous when it comes to attending interviews and you are no exception. The only difference is that they handle them a bit smarter and even you can do it, by overcoming the minor glitches to handle such situation at ease.
Wish to give couple of suggestions that might help you overcome this bottleneck. You can team up with a smart friend closer to you to conduct some mock interview both technical and non-technical and ask him or her to give a feedback in writing. On review of the feedback, if you find that the comments given by your friend is true and entails action from your end, then you need to overcome it but by your constant efforts to improve upon them.
You can do a self-mock interview by standing in front of a mirror and try to imitate the character of both the Interviewer and yourself; this will give you a fair idea of the gestures and body language, which is one of the key ingredients to perform well in an interview.
To improve on your communication skills, learn the trait of listening and then responding to situation. Be circumspect and conscious when you make a mistake and ensure you do not repeat such mistake again, this will infuse confidence in you. You can also watch English news or business channels, in particular where panel discussions take place. At the meantime, it becomes necessary for you to jot dot some important words, terms, phrases that you can check for its meaning and use it in your conversation, so that you can sound more confident and assertive.
Some quotes to pep you up:
Learning is more effective when it is an active rather than a passive process
Euripides quotes
There is only one thing more painful than learning from experience and that is not learning from experience.
Archibald MacLeish quotes
Every act of conscious learning requires the willingness to suffer an injury to one’s self-esteem. That is why young children, before they are aware of their own self-importance, learn so easily. ~Thomas Szasz
You can teach a student a lesson for a day; but if you can teach him to learn by creating curiosity, he will continue the learning process as long as he lives. ~Clay P. Bedford
Best of luck
Sathish