Fundamentals, Cycles & Trends (FC & T's): Your plan, if done in advance and thoroughly, should provide and excellent foundation from which to work. Even the best plan still has to react to outside forces that will influence your best intentions. Identifying certain fundamentals, cycles and trends that may impact your company is a prudent way to being able to develop a contingency "plan B" in the event an outside force rears its head. A series of key FC & T's should be monitored throughout the year so that if required, your plan can react. Certain FC & T's may include wholesale pricing, weather, commodity markets or labor market impacts that are out of your control. In my opinion, developing contingency plans in advance for these outside forces at least gives you a fighting chance to react favorably.
A lot of resources nowadays provide ready_made plans for specific businesses and whilst this is handy, most business owners will recommend that you write the plan yourself. This is because writing a plan for your business actually forces you to focus on what you want from your business and how to achieve your goals. When looking back on your initial plan for reference, you shouldn't necessarily assume that your initial assumptions and predictions will be correct, they are just that: predictions. You should be able to go back to your plan on a regular basis and view it and change it to relate to the actual current situation.