Understanding a Work Breakdown Structure
Microsoft Project uses the term Work Breakdown Structure (WBS) to mean a hierarchical list of working activities. The tasks you create in a Microsoft Project schedule are really an Activity Breakdown Structure (ABS) showing the relationship of tasks throughout the schedule.
The term WBS has a formal definition and United States government MIL-HDBK-881A standard. That standard describes how a WBS is used to define the cost and management control structures that define the official scope of your project. Even though this is a government military standard, project management discipline has adopted this standard as the basis for defining a Work Breakdown Structure. You should review this standard to better understand the distinction between Activity Breakdown Structure and Work Breakdown Structure.
You should also consider reviewing ANSI/EIA Standard 748 that defines Earned Value Management (EVM) and specifically refers to the formal WBS definitions. EVM is a well-defined strategy to clearly determine how your project is performing against defined Work Breakdown Structure scope.
Use your favorite Internet search engine to learn more about WBS and Earned Value Management.
Define the Full Scope of Your Project
When building a schedule, it is always easier to add more detail later than to take it out. If you keep your schedule focused on deliverables, it will be much easier to identify deliverables that have not been fully defined. This allows much greater flexibility in setting the scope for a project. (This is accomplished naturally if you follow the best practice of creating a WBS prior to creating a schedule! It is extremely difficult to keep WBS principles in mind when you jump to creation of a schedule without having gone through prior creation of a WBS.)
Build WBS First
Many project managers skip the process of building a WBS before they build a schedule because project sponsors tend to push for early resource and date commitments. Microsoft Project is an excellent scheduling tool, and it can be an excellent tool for controlling scope if the Project Manager takes a disciplined approach to developing a WBS from the beginning.
Avoid the tendency to structure your schedule according to workgroup during initial decomposition because it will limit your thinking and make it much easier to violate the 100% rule. Focus on the work to be delivered, describe it completely in a WBS and WBS dictionary, and then assign the logical flow of precedence and the resources. Other fields can be used to structure your schedule according to workgroups, GL codes, and so on, after the WBS is complete.
Define Project Work Packages
Understand the work package level of your project as the most important component for providing scope management and control. This will keep you "out of the weeds," and you can make decisions based on the impact to the work package rather than trying to deal with many activities. You can rearrange work packages in a variety of ways and still be assured that the scope of the project is accurate. There is no single correct structure for WBS; work packages can be arranged in a variety of ways.
Make sure that all of the work packages within your project support the defined measures of success and that you have an objective method to measure both progress and accomplishment of the project goal. Most project failures are due to not understanding or managing scope; project success requires a clear goal and a scope of work that supports the goal.