How to comfortably talk to anyone
Man, that's a big question-- you're going to get a dozen great answers, I'll bet.
I've interviewed dozens of people over the years on camera... this is where I've had to walk up to someone, completely "cold," and try to make an intelligent conversation with no awkward pauses. With a camera on me. No pressure! :-)
Along the way, I've learned a few tricks. Here are my suggestions:
Try to not be self-conscious and focus on the fact that you can't think of anything to say. It'll distract you and cause you to clam up! I know that's easier said than done, but here's really what I mean: instead of listening to the voice in your head saying "omg omg omg omg what should I say next?," listen to who you're talking to and think about what they're saying. It will help your brain make connections to other things that in turn will give you ideas of what to talk about. It works best when you just open your ears and listen up.
Instead, look for open-ended conversation questions and things to discuss to help draw conversation out of the other person. Remember that conversation is like a ping-pong game... you pass the ball back and forth. Talk for a moment and see what the other person can offer. If they don't have anything to contribute, think of a question you can ask them. Try to find a question that isn't yes/no. If you can't think of anything else, try a yes/no question ("do you have any brothers or sisters?") but then see if you can follow it up with a natural response that might draw the other person out a bit ("oh, you don't? do you ever wish you did have brothers or sisters? why's that?").
In most cases, asking someone what they do for a living is a boorish way to prompt conversation (you can get away with it in many situations in the USA but it's still kinda lame). Focus on other things to talk about. One of the easiest is to look around and talk about how you got where you are. If you're at a party, ask the other person how they know the host, or if they like the music, or what the best party is they've ever been to, etc. If you're on a date, talk about how you met the other person, talk about what you like to do in your free time, ask him/her what they like to do in their free time, etc. If you are at a function related to your career--for example, a meetup for coders, talk about how you found out about the event, or about how you started coding, or your favorite text editor. :-) Just think about things that make sense to talk about in the context of where you are or how you got there and it can naturally give you stuff to talk about.
Bonus points: think about those things BEFORE you event. So if you know you're going to a party tonight at your boss's house and you'll meet new people that you'll want to chat with, think about five go-to topics before the party. Then you'll have some things "in your pocket" to talk about when you get there.
Coffee helps. Alcohol, too, but not too much.
If there's a natural opportunity to join an existing conversation, take it. Not only does this let you do "less work" (since the others will be talking as well, it means less that you have to do), it also means more opportunities for you to hear something that prompts you to say something. In other words: a bigger conversation (when you are amongst 3, 4, or 5 people) lets to talk less but also gives you more chances that you will naturally be able to contribute.
Finally, and maybe most importantly... don't forget this one!... making conversation is a skill. It's best practiced. Like any skill, it means you probably won't be great at it initially, but the more you work at it, the better you'll get. Soon people will be admiring you for your natural conversation skills, and your ability to talk to anyone. :-) So practice whenever you can! Strike up a chat and put yourself out there. Sometimes you'll fail and be flummoxed and have nothing to say. That's ok. It's part of the process. Don't beat yourself up or think you're stupid... you're not... remember, it's a skill! You will get better with practice, I guarantee it.
Good luck!! Making conversation is one of the most powerful and useful skills you can have. Good for you for wanting to improve