Compartmentalizing your plan by developing planning modules allows you to attack the plan in parts, yet still maintain a cohesive plan. I have found that developing an annual plan made up of quarterly targets - thus becoming a rolling quarterly forecast financial model - allows for a cohesive structure along with the nimbleness to react to market conditions. At the end of each quarter, a true-up process to align results to annual targets needs to be re-forecast and adjustments made.
At the end of the year, a thorough review of the plan and its process should be discussed with the team in order to make the next planning cycle more effective and efficient. Take a look at all of the successful initiatives and the ones that fell short in order to identify where the broken pipes occurred in the process.