I used to be incredibly socially awkward, I would struggle to join in or start conversations. It felt like I was always thinking of what to say, so I'd even have a response ready in my mind but felt like I'd "missed my turn".

Then I started a business and through meetings with clients I was forced to talk to a lot of strangers. This really helped, so, honestly it's just practice.

Now I can just walk up to someone and say "Hey, how's it going?" Or "Good morning, how are you?" And most of the time the conversation just flows naturally to "how have things been/what have you been up to lately/how's work" etc.

An important thing to remember is that most people want to talk about themselves, if you give somebody the opportunity to tell you about their life and you show genuine interest, they'll keep the conversation flowing.