Here the students should develop an intuition of where the charge will go based on electrostatic repulsion/attraction combined with the fact that charges flow freely in conductors. If repelled, they will move as far away as possible, etc.
Conservation of charge comes into play for charging by induction. If one removes charge of one sign from an initially uncharged object, the object becomes charged with the other sign.
Tipler 22-80
Coulomb's law
Electrostatics ties in with mechanics, (one of my favorite games to play in exams!)
Look for fundamental difficulty with setting up mechanics problem
Do the students grasp the fact that the solution to this problem involves a balance between the electostatic force of repulsion and the gravitational force?
Are they able to write down a diagram for each ball with all of the forces?
Do they understand the best way to solve a pendulum problem is by breaking forces into components along the supporting string and perpindicular to that?
Are they comfortable with a problem with no numbers?
For exams I will give most credit for the ability to set up a solution correctly. Plugging in numbers at the end will earn very little, on a relative scale.
Tipler 23-42
Gauss's law
Use of symmetry to simplify problems
Interpretation of the fields in the final answer (for r<R, get cancellation - for r>R, looks like an infinite line charge)
Do the students see the symmetry in this problem that leads one to choose cylindrical Gaussian surfaces to solve it?
Do they understand how the symmetry simplifies the problem of dealing with the "endcaps" of the cylindrical Gaussian surface?
Emphasize that the students should ALWAYS look at the final answer to see if it makes sense. Sometimes it is very useful to look at limiting cases, particularly when that simplifies to a case where you know the answer. In this case, look at the case when R gets very small. This should simplify to the infinite line charge case covered in the text.