Reading: GVC § Gauss's Law and Symmetry–More Gauss's Law: Cylinders and Spheres

most students remember something about this law. This makes a nice “recall” SWBQ. Ask the students to write down Gauss's law on their small white boards and then construct the answer on the front board from the bits and pieces that they remember, emphasizing why each of the pieces is important and talking about the geometry of each piece.

emphasize that Gauss's law holds for ANY electrostatic field and ANY (imaginary) surface

most students will look for a real surface in the problem, rather than an imaginary one. Emphasize this. (Try the following and add it as an activity if it is effective.) Maybe it would be worth giving them a charge distribution and asking them to draw the Gaussian surface that works. Collect a bunch and then emphasize that they all work.

do the example of Gauss's law for a thick plane of charge, modelling the symmetry arguments involved.