The method proposed in this paper is simple for beginners to draw an appropriate Lewis structure, its resonance forms, as well as isomers. The algorithm is based on straightforward mathematical calculations and is easy to understand for beginners, especially when the molecular complexity increases because the number of multiple bonds in a molecule is easy to be determined by this approach. The approach is the direct application of the octet rule. However, it can also be applied to various species violating the rule, such as some types of odd-electron molecules or ions. In addition, it does not require σ/π concept prior to Lewis structures, so that students will not have conceptual difficulties when using this method.