Using rule 1: A positive test charge is attracted directly toward a negative point charge, or repelled directly away from a positive point charge. Electric field lines must point radially toward or radially away from the point charge. Using rule 2: The spacing of field lines indicates the magnitude of the electric field. The magnitude of the field due to the point charge depends on the distance from the point charge. So the spacing/density of the field lines must look the same at all points at a certain distance from the point charge. Using rule 3: A positive point charge has field lines that originate from it. If the point charge is negative, the field lines terminate on it.
Work Step by Step
Conclusion: the lines are radial and their spacing is constant for a given distance from the point charge. They must be symmetrically located around the point charge.