Given a radius and center, students will write the Standard Form equation of a circle. They will expand that to write the General (Conic) Form equation of a circle. Also, given the equation in General Form, students will complete the square to write the equation in Standard Form.
Standard: (x-h)^2 + (y-k)^2 = r^2
General: ax^2 + by^2 + cx + dy + e = 0
I've used this in my class after my students are comfortable using General Form. This helps them be able to distinguish between each form.