[susan53]

I don't think you can expect people to "think" spontaneously in the language until they are at a fairly advanced stage. However, I do think it's useful to get them to think through what they want to say before they actually say it - a technique I call silent planning, though I've also seen it called "Inner Voice". Basically, before the students say anything, you ask them to plan what they want to say in English. Say for example you want them to have a discussion on "What did you do at the weekend?". Before putting them into pairs you would ask them to close their eyes and visualise themselves having the conversation, thinking about what they want to say, what questions the other person might ask, how they would reply, etc. They are trying to get a mental image of the conversation, in English, but also to identify anything that they want to say and can't. After the visualisation, they then have a chance to ask you for the missing language, which goes up on the board, before they actually start talking.
This is very similar to what a lot of sports people do - tennis players for example may visualise hitting the ball perfectly - the idea being, that if the brain creates a mental image of how the action "feels", the body will carry it out automatically in the real situation. I'm trying to get the students to do much the same thing.
The example I've given presumes a certain level, but I start the work right at beginners level - even when I'm doing repetition work, I ask the learners to repeat the utterance silently in their minds before repeating it chorally - again, to create the mental "feel" of the language.