I made a whole bunch of friend on Yahoo MI, most of them just started to talk to me and I answered. Just go over people's profiles and see who looks like they might be a good friend, check to see if you have some hobbies or other things in common and just start a conversation. It's good to start it with stating what it is you are looking for and not just as if you and the other person are already friends. Something like "Hi, my name is.... I'm...years old and love music and reading science fiction books, I want to make new friends and learn more about you, do you want to chat with me?"

Some people will not answer back, don't be hurt by that, a lot of people uses MI just to talk to friends and people they know from the offline world,  also, some people are cautious and would not talk to a stranger (especially women).

Try to be polite and nice, ask questions and talk openly about yourself without being pushy (if you are looking to meet women, asking for a picture or video chat early on is rude and a big turn off).