How do i improve my communication skills?

I am a person who is comfortable only around close ppl...and the list of close ppl is really small like really really small... And talking to strangers gives me anxoety like how will start communicating or wht will i talk with them how will i do so...what will they think i dont know why this sounds so simple to some ppl bt i really find it as a massive task-COMMUNICATING WITH SOMEONE... for example whenever i get calls from unknowm numbers, it feels more stressful to attend it..So if anyone can suggest any tips, it would be very helpful for me..