First, a serious one - I practiced out loud the conversations I wanted to have or the things I wanted to be able to talk about. This technique has, literally, saved me. It's better than shadowing or imitation because you're practicing the things YOU are interested in or YOU want to be able to say, not just a random conversation (although shadowing and imitation are good practice for pronunciation and intonation). It helps you identify the vocabulary or grammar structures you don't know, so you can look them up, and then because you practiced actually saying them, it's easier to say them in a real conversation.

Second, a less serious one, although this did actually work for me - be in a country that speaks your target language and go to a bar. Drink a few drinks, so you don't feel so worried about whether you'll speak perfectly or not. Strike up a conversation.

Many or much