I would propose that you write out a few phrases that you are likely to use in a coming conversation and learn them. That gives you a few supports to help you into the conversation and gives the other side a little confidence. Sometimes I find myself groping for a word (many times) an have a "cheat sheet" by my side very useful Practice

I like Bill's ideas about phrases that you are likely to use and the use of a 'cheat sheet'. I also appreciate Khaled's idea about not being shy, allowing yourself to speak like a child ... fearlessly. Fluency means two things: a)being able to speak easily and articulately b)freeflowing. I would imagine that nerves probably get a hold of you while chatting and this results in searching for words in your mind. So, relax and enjoy the act of communication. Don't worry about getting stuck, or searching for a word. People get stuck all the time while speaking their native tongue. If you get stuck, try and make a mental or physical note of where, why and how. Did you need a different connective? A subject specific word? ,,,? If you make a note of it when you come to a block, simply have a go at writing a few sentences in the notebook using the words/phrases. There will be corrections, if required, and you can use your new vocab in your next conversation.

in my opinion, The best way to learn any language is to practice a lot. Speak, write, read and listen a lot ... these can help you to learn any language you want ... For example, you learned the Arabic with practice and you didn't be shy when you said something wrong in your childhood ... so don't be shy and practice a lot xD