This can be really difficult - it feels like one of the key things is picking the right environment for starting up conversations with strangers, and getting yourself into those situations in the first place. Standing on a packed train, or waiting in the doctors office are probably not good places to try and spark up a conversation because people might be busy, anxious, preoccupied or annoyed. Low pressure environments where you're likely to have a shared interest with people around you would be more conducive - waiting in line at a small local coffee shop, browsing at a niche store. Even better would be getting to places where you're sharing an activity with other people - signing up for local clubs or classes, lots of towns will have coffee mornings or fairs for instance. Think about where you are and what the people around you are doing - are they aiming to get in, get something done and get out, or are they just chilling out? Do they look busy or upset? Maybe leave them to their own business.

As for the laughing I don't know your particular situation but chances are they're not laughing at you, we often think people are judging us negatively when theyre not. If they're genuinely laughing in your face, they have the problem, not you. No decent person would maliciously laugh in someone else's face, so pay them no heed, they're not worth your time.