What kinds of things can be used to represent the air element in spell casting?

Just have Dust in the Wind playing in the background

If you are looking for altar correspondences in western ceremonial magick it is mostly incense of some type. In the hermetic systems you have the air dagger as the ritual tool which is made through specific use and formula in those systems. You could also use the ace of swords or the alchemic symbol for air.

If you need more examples for the other elements and planets this has examples of those for the tarot.