1. Keep practising. You’re vocabulary will improve. The more you use it the more it begins to flow. In the beginning it might feel like you are making it up. Go with it.
2. Keep describing until you’ve finished. Whenever a new image begins to replace the one already there go with it. This is why it’s important to talk quickly. Don’t try to understand the image stream until you’ve finished. That’s why you should talk to a tape recorder.
3. Keep working at it. Remember the person you’re telling it to doesn’t see your image stream so if the floor is covered with carpet you need to describe it so they could see it. It’s the same as describing the birthday cake you had at the last party. You could practise image streaming by remembering something like that and describing it out loud. In so much detail that you could taste, smell, feel, hear and see the party again.
4, In Australia there is a bird that does perfect imitations of the sounds they hear. We can’t do that as well so we would describe it by using saying a bark, going further into what type of bark, growing, high pitched, deep, frightened, happy?

More detail, don’t worry too much about the right words they are coming from the same source as the image stream. As long as you keep describing without analysing you’re on the roll.