The first step is Discovery. This is the time to sit down discuss the issues and outline the goals. Sure, it seems obvious, but this stage is often neglected or bypassed all together in a mad rush to "get going." The most crucial thing at this step is to define--and agree on--the problem. Skip it and you'll find yourself coming back a few thousand dollars later.
Next comes Strategy. This is the point when we establish parameters and logistics, and develop a blueprint. What are the job's requirements, when and where is it due? Most importantly, how will we define its success? The strategy determines what will put your audience into a favorable frame of mind, or induce a particular course of action, and provides direction for creative execution.
Once the strategy is in place, the next phase is Creation. With the content outlined and the goals defined, your message requires a container--a structure or vessel that will carry it to your intended audience. The form of this container matters a lot. Going back to the architecture analogy, the floorplan, materials and location of a building are determined according to its plan; and the plan is based on the building's intended use. See how this stuff just links right up!
The final step is Evaluation. Was the project on time and within budget? Did you meet the goals described in the discovery phase? What lessons could be applied to future projects? For on-going campaigns or projects, this is a time to measure and fine-tune.
Of course, in the real world not every piece of every project gets the full measure of every step in the process--stuff happens. But without solid guideposts, projects risk ineffectiveness or worse. From simple spot illustrations to complete brand identity systems, structure matters--in the project and in the process.