There are five primary workflows in software development project:
Requirement Capture, Analysis, Design, Implementation & Test.They are all important, however you must ensure that you schedule enough time for the analysis & design phases.
During the analysis phase you define the what the system is suppose to accomplish. You do that by defining the set of actors(users, devices and the other systems that interact with the proposed system) and activities that the proposed system must accomodate. Also the Analysis phase must identify the domain objects(both physical & conceptual) that the proposed system will manipulate and the behaviors and interactions among these objects. These behaviors implement the activities that the proposed system must support. The description of the activities should be detailed enough to create baseling criteria for the Test phase.
During the Design phase you define how the system will achieve its goals. In this phase, you create a model of the actors, activities, objects and behaviors for the proposed system. For this class, you use the Unified Modeling Language(UML) as your modeling tool.