This has taken me a very long time to realise, but the pressure to have something to say and say the right thing often silences me and makes me quiet and unable to speak

I found and find that if I can try to just keep slowing my mind a little by letting go of negative thoughts saying "release pain" and feeling it really helps

Don't pressure yourself - the pressure stops you being able to think of what to say -  its learning to reduce that pressure and act very slowly that lets spontaneous and interesting thoughts pop up (It feels very slow, to other people it looks normal / confident). Acting slow makes you think slow. Thinking slow calms your mind down, calm mind thinks fast and of interesting things.

Then in a conversation dont worry about what to say, just 'feel' and 'imagine' what the other person is saying and relax your body a lot. When you do this little things will please you and you will naturally find them funny and laugh a little - people LOVE this. Everyone is quite insecure, and when you hear something and it makes you giggle without meaning to it is a sign to the other person of social approval. 

Slowing and listening also means you 'get' when the right time is to say things much more easily, rather than the "I make a great joke... and no-one seems to hear me" situation 

Keep forgetting your body is there. Keep slowing. Keep absrobing and listening.

I astounded myself a few weeks ago keeping conversation and social going with 3 people I didn't know that I considered very high-risk and one of them texted me to say what a lovely person him and his wife thought I was and invite me to his BBQ (which I declined because I find people hard).

We think it is all about 'being cool' and saying the right thing and so on and beat ourselves up. It's more being in a more relaxed mindset, not focusing on pain. 

Try it and see what happens