The following diagram summarizes the components of valuating a stock fundamentally. While most of us just concentrate on the Income statement, there is a need to go one level down and understand what influences those sub-components and their trajectory.
The difficult part is in guaging the P/E multiple. Whatever numbers we come up with for earnings growth rate are just estimates as we are trying to predict the future. We need to understand the company, its products, competitors, new developments in the sector etc. to get a reasonable estimate.