I do it this way: when I go to the shop, I try to say in the language I learn things like where I'm going to, what I want to buy, I try to enumerate as many things that come to my mind (without exaggerating though), etc. That helps me practice and see if I acquired enough vocabulary to have such a sort of conversation.
Sometimes I just have a chit-chat with myself while walking, be it in Portuguese, be it in Arabic or any other language.
In my opinion, this kind of practice is very important, especially when you don't have native speakers in your family or among friends. Of course, I'd rather drill vocabulary connected with everyday situations than scientific disputes. Other useful subjects may be: your hobby, likes and dislikes, your favorite writer, asking the way, buying a bus ticket, etc. etc.
Usually, I do it aloud to hear the sentences coming out from my mouth. It's kind of simulating a real-life situation. I call it "walking like an Arab" or "walking like a Portuguese" and so on, in a metaphorical sense. I'm conscious that sometimes - when I forget that I'm talking to myself on the street - I may be taken for a crazy person, but I don't care. As long as it suits my needs, why should I bother?
In fact, don't people more and more often look like they were talking to themselves, when they are calling someone, for example using mobile and Bluetooth? And what about Google Glass? It seems that in the future it won't be so extraordinary to see someone walking and talking...
Do you practice your languages walking and talking to yourself?
(Photo: Rana Sawalha - Unsplash)