Here are some great tips from the All Things Linguistic blog:
1. Pre-think. What kinds of situations am I going to be in? What will people say/how will I respond? Basic situation ideas include: where/how you learned the language, where you’re from/what you do (and other biographic information), what you’re doing in the area and for how long, especially if you’ve travelled there to learn the language. Also think about how to describe things you’ve done recently or are planning to do. Think about who you’re going to see and what you could say to them. If a funny thing happens to you, describe it to yourself in the language, so it will be easier to tell someone else about later. This is a great time to look up how to say essential words.
2. Re-think. When you have a conversation in the language that goes less-than-ideally, or where you had to switch languages, afterwards think about how you would have said things in the language so if the situation comes up again you are prepared. If you are trying to learn a language with few speakers around you, then you can also do this for any conversation you’ve had. This is also a good time to look stuff up.
3. Learn filler words. Every speaker hesitates sometimes, so learn the equivalent of “ummm” and “ohh” in the language. Similarly, learn transition words/expressions like “and so”, “and then”, etc. This signals that when you don’t know what to say, it’s a content issue, not a language one, so people will be less likely to switch out of the language.
Check out the rest over there…