How do you make friends out of strangers?

I'm trying to break out of my shell and have challenged myself to speak to someone new every day (which is very hard when you're not that outgoing), but so far I have been able to strike up minor chats at the gym, at school, and at the grocery store with people that I see on a daily basis and rarely with just random people that I'll probably never see again.

Anyway, I'd like to open my mouth more and meet more people with the goal of making more friends. I've had the same friends since high school and I'd like to broaden my social circle or whatever. For those of you who are really good at meeting people and making friends in new situations like let's say a party or an outing, what kinds of things do you do to start or make long-lasting friendships with new acquiantances or strangers?

I try to strike up some small talk like the weather or something going on in the news with people, or if it's people I see regularly like at school or the gym, I'll try to talk about things related to the school or working out, etc. I try to smile and be pleasant, and people reciprocate by chatting with me for a little bit, but I guess they're just not interested in making a new acquiantance or friend.

Sometimes when I try to get people to talk, it feels like I'm doing an interview and they just don't open up. Are there any surefire questions, conversations, things I could do, etc. to help my chances of making acquaintances or friends with new people? For the people I see daily, I sometimes try to invite them to hang out or whatnot, but they never seem interested. Maybe I'm just too boring?

Jam it back in, in the dark.