As they say, join interest groups or when you're at your job or such. When you're there, start out by looking around for something interesting, unusual, or that you are likely to relate on.
For instance, if you worked at a supermarket, you could wait until you had to talk to a colleague for a legitimate reason, like asking for a customer where something is. Then once that's done and you're still standing together, you tell them about a funny customer you had that day: 'at least that request was normal. I got one a few days ago about...'. This then let's them laugh along, and they'll probably have their own story to say.
You tell them 'well, I'd better get back to working - we should carry on talking sometime.' This gives you an opening to talk to them again whenever.
You can do the same in interest groups. For instance, you're in an arts and crafts group working on your projects. You ask the person beside you 'hey, can you pass the glue?' they do. 'Thanks. These things are really hard to stick down, eh? How are you going with your project?' Again, it starts a conversation and at the end you can ask if they want to talk again sometime, or if you see them there regularly just talk there for a while first.
The trick is to say something with a smile on your face - funny, or even laughing at yourself/what you're doing and to open up the line for them to respond. Try to keep the anecdotes short to start with so they can reply, and listen hard to what they're saying - don't feel like you have to respond with a proper sentence.
So - practical small reason, barely linked funny thing, let them reply, continue talk later. That's my formula. 
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Curiosity is more virtuous than virtue ~ Michael Vassar (president of the Singularity Institute)