Deconstruction is post-structural, which means that it takes structuralism seriously as an analytic technique, but questions its rigidity and methodological character.
1. The interpretation of a text is never "closed". Since texts can re-arrange themselves, one can never come to the "true" interpretation of a text.
2. Meaning is not determined by figuring out what a word points to ("metaphysics of presence"), nor by appealing to a stable meaning of a word ("logocentrism").
3. Meaning is tied to textual freeplay. Derrida often uses puns, the intent of which is to show that words have different references depending on the influences we read in the text.
4. Intertextuality spreads from texts to all understanding. In postmodernism, things make reference to other things. The collage is an important image. Incongruous things are put together to make new associations. "Cut-ups" were popular in literature -- computer programs that took units of writing from a text and reassembled them. Something could be written "in the Joyce style". In art or architecture, incongruous elements put together asked new questions about capitalism, the use of space, religion, or whatever.