Some looser stuff that'd probably be hard to apply:
Causality - Dreams have SOME form of cause and effect, but they are linked by symbolism, and loose in target. When you close a door, something else closes. When one thing breaks, so does another. Some forms of sympathetic effect or side effect could be possible, some part of manipulating a dream involves identifying how the abstract and the material are connected, and then altering one to change another.
Symbolism - Relating to the above, you then need some way to organize themes, if only by keywords. A happy dream for example, might be associated with positive imagery in the dream itself, bright, warm things, or living things, so to affect the entire dreamscape, you only need to find the strongest anchor to it's image and contaminate that. Likewise, bringing a thing into it's antithesis can have either one swamped and transformed, a candle might banish the dark, or it might be consumed, the only factor is the belief and symbols placed into it. Might have application in dream-focus objects and auto-suggestion props, condensing particular memories and belief into things that are more real than the rest of the dream.
Scale invariance - From the above, size doesn't matter across categories, only within categories. The image of a mountain against a rampant dog might be equal, but a dog with a dinosaur is not. I'm not entirely sure where I'm going with this though.