First of all try to understand that your fear is not based on anything. You are surrounded not by evil detractors who are specifically waiting for your misstep to raise for laughter, but ordinary people just like you. And as for possible mistakes, even geniuses are not immune from them.
To be guaranteed not to get into awkward situations, engage in conversation if it’s about things you’re well versed in. In cases like this, the probability of error is minimal, and being aware of it will give you self-confidence. Fear will gradually begin to recede, and you will be able to sustain conversation on almost any topic. If it is boring or incomprehensible to you, limit yourself to short, neutral phrases. The main thing is don’t keep quiet.
A very good way to overcome your fear of communication is to act on the principle of “wedge bouncing”. Since you are frightened by the need to talk to other people, literally force yourself to do it. Please contact the seller in the store, the ticket cashier, the on-call employee in any administrative institution. Try to engage in a conversation with anyone: a neighbor walking a dog, a fellow worker at work, even if you don’t really complain about him, a random fellow traveller in a train car, etc. two or three short phrases, on the most neutral topics, for example, about the weather. You very soon make sure that talking to outsiders is not scary at all. And after that, you can already move to longer conversations.
If you still find it difficult to communicate, try to overcome your fear with phone conversations or Skype communication in voice mode. Without seeing the interlocutor, it will be easier for you to get used to the idea that there is nothing terrible about talking to outsiders!