Human beings as individuals have varied personality traits and unique nature. Some people are extremely introvert - who hesitate opening up and are quite reserved in a group whereas some are extroverts - exactly opposite to the introverts, they share their thoughts openly among groups, are more social and show confidence in their attitude.
Introverts do not feel comfortable when they are in a group, they feel awkward while conversing with more than 2 or 3 people. They feel shy to put up their thoughts in front of a mob. These traits are partly hereditary and partly a trait of an individual's personality. Know to feel comfortable with yourself so you can make people around you feel comfortable.
No one can master art of conversation overnight. You should be patient enough to accept what you lack and ready to change yourself accordingly. Here are a few suggestive lines, working on which, you will be able to change yourself from an introvert to an extrovert.
There is an interesting concept called "breaking the ice" which means one of the two strangers breaks the silence and initiates a conversation. You need to understand that till now, you faced difficulty to open up with people because there was lack of initiative in you.
If you try to initiate a conversation with a stranger wherever you go, you can develop a habit of making friends and start getting comfortable with them easily.
Do not hesitate to share real life incidences/experiences with people around you when you feel that you are in a good company. You are mature enough to understand people and judge them.
Be Positive in Your Expression
Even if you have to share a negative thought or any tragic situation of your life or any issue in general, be soft, calm and mostly make use of words that reflect positivity. Results into a healthy talk without disturbing others' mental stability. You should always think what you want to say before saying it. This will help to avoid controversial statements.
A smart person is able to identify the artificiality in your conversation quickly, especially when you praise him/her. So be alert and praise the person honestly.
Do not Make Fun of Others
We have no idea if people take things positively or get offended. So to be on the safer side do not try to develop proximity by making fun of others. Instead try to make fun of yourself. This will project you as very realistic and humble personality.
The person conversing with you must not feel that you are only hearing and not listening to him. This will disturb the flow of conversation as you won't understand what to say next. Listening is also a good way to have an idea of the views that others have about a specific issue and their general perspective while analyzing things.
Lastly, try to be yourself. If you behave naturally and do not exaggerate unnecessarily, people will like you and want you to be around. Follow these tips and see what difference it makes to your personality. Good luck!