To apply Gauss's Law for symmetrical electric objects like an infinite cylindrical shell, it is essential to choose an appropriate Gaussian surface that aligns with the symmetry of the problem. For cylindrical shells, the Gaussian surface should be coaxial with the cylinder, allowing for the electric field to be uniform across the surface. The contribution to the integral of E·A comes only from the faces of the Gaussian surface that are perpendicular to the electric field, as parallel faces do not contribute. Understanding the symmetry helps simplify calculations, as the electric field magnitude remains constant across these perpendicular surfaces. Mastering these concepts will aid in resolving electrostatic problems effectively.