Personally, I've found that, and as rude as it sounds, but involving yourself in other people's conversations around you, can get you miles!
Whereas in the 'regular' world, you butt in to a conversation and you will get a short, stunted conversation, where they clearly are uncomfortable with you. At conventions, people are just so much more relaxed about being approached by strangers. But that is how I met most of my friends! 99% of con-goers I have met are so lovely and we have great little chats, which we continue online after the con and it goes from there.
Another way is just not being afraid to chat to someone if you ask them for a photo. I mean if they are obviously in a rush to get somewhere then leave them be, but I find it common courtesy to show them a photo after you have taken it, and that is the perfect window for chit-chat, and it gives you your starting questions to get to know them [how long did it take to make? how much of the anime/manga/game/etc have you seen/read/etc].
The only thing I will add is not EVERY con go-er thinks this way, as obvious as this might sound. Some people, and I'm on about the tiniest of minorities will not be accommodating and won't appreciate it, so at the same time as not being scared of approaching people/being approached, remember your stranger danger, and if they seem really tense/nervous/angry, cut it short and walk away.
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