Practice, practice and practice in front of a mirror, family and friends, use a tape recorder, *talk to lots of people everywhere they go (I personally use this one*) and if possible attend several Public Speaking Seminars.
When in line at the store just smile and say hello to the person next to you. Or compliment them. If you like their jacket tell them. If they are buying something you are interested in, ask them about it.
Drink alcohol and answer the phone when a telemarketer calls.
Answer the door when a Jehovah's Witness is distributing their Watchtower pamphlet, invite them in for coffee.
Get small bills and spend the evening at a strip club getting lap dances.
Color with an inquisitive child, or have said child teach you how to do something new.
Read a book out loud.
Start off with saying small things like "it's a lovely day" or "how are you?" If you meet people familiar t you . If you aren't involved in any actuvities like a book club or a sports club like football, tennis or soccer maybe try something like them. You are meeting people and you often start talking to others without you realising
Start drinking it worked for me. Lololol
Get a job, specifically a sales job. At Nordstroms or something if you're young. Your sales will be ranked against your peers, which will force you start conversations and start forming strategies on how to talk to people. Plus the better you talk to people, the more sales you make, and since Nordstroms is a left-leaning company you get paid commission. Which means more $$$$ the better you improve.
"...some of the techniques.....used to use to help people become better public speakers could also be used to help shy people improve their conversation skills."
Much more here:
http://www.selfgrowth.com/articles/how-shy-people-can-improve-their-conversation-skills
Never underestimate the value of a good listener. If you allow yourself to be truly interested in what the other person is saying, responses will come automatically.
How should I know? Chances are I'm shier than they are...
Get used to reading someone's body language while you are talking to them. Their expressions, their demeanor can tell you more than their actual words.
In addition, don't monopolize the conversation. Ask questions - be interested in other people
Look them in the eye when you are talking to them.