I like that you're honest about not being able to be relaxed and spontainious in conversations. Other people just pump themselves with confidences and do all kinds of stupid things.
Conversations are like art. You have to be completly in the moment, spontainious, at ease, empty minded, improvisational, expressive. Not full of techniques, and a list of prepered jokes and stories in your poket.
Meditation is The nr. 1 solution.
If you stay honest about your problem, you will overcome it.