How to be chatty, talkative, be better at conversations and talk about just anything?

I am really poor when it comes to making conversations.There are times when I want to speak but have no idea what to say,I feel so miserable.And when in a group I can barely open my mouth.
How can I be very very chatty, very talkative?
How to make really good conversations and prevent them from dyeing out?
And what can I do when some group I join is already talking about something?
Any books you would suggest? Any online resources or videos that can help me? Internet is a great source for almost anything,provided we can search it well.