Feel Good About Yourself
The only person we get to be in our lives is us. If we can't like ourselves for who we are, how can we expect anyone else to? Accepting who we are, loving ourselves, and embracing our quirks literally liberates us of our inhibitions, and helps us become a more confident individual.
While striking up a conversation, the right approach is the key. Perhaps, the most important factor in approaching a group is about how receptive it is. Certain body languages, in such cases, are the cues you need to look out for.
In a group that doesn't seem very receptive, you could strike up a conversation with one person who doesn't seem very interested in the ongoing topic, and slowly make your way into the group. Another way is to strike up a conversation with a member of the group while he/she is away from the group. A handy tip would be not to do that when the person is scrambling his way to the johns.
We totally understanding how intimidating it can get when you have to take the initiative to join a conversation. These pointers will definitely be of help; all you need to do is to be confident and practice.