Is it just imagery coming to you while you're still in control of your waking body, or are you able to move in this small undefined dream? If you're still in your normal body then do what others here have suggested, but if you're able to move in the dream already then you can try various techniques like rubbing your hands together, spinning, touching objects in the dream etc to solidify and clarify the dream. I've often had dreams that seemed so distant and blurry but a little rubbing my hands together would make them as clear as day.

I tend to find though the lesser the clarity of the dream, the harder it is to move inside the dream (sometimes being completely impossible), this is why I rely on hand rubbing the most since for me personally when movement gets harder in a dream my hands are usually the last thing I'm able to control before I can't move at all or wake up.