This topic is very broad and so nothing beyond a very broad overview is really possible to give a very basic overview, namely where to start or begin, in the hope that this gets the process going. More specific questions may also have significant answers.
Before you begin
Who are you writing the business plan for? What do you want out of it? Different people have different styles, and so there is some room for disagreement in overall structure if you are not writing it for investors but you need to get this question answered in your mind first.
Possible answers for "what do you want to get out of it" include:
- Clarity of vision regarding the market and business options.
- Motivation to get started, and
- Focus for actions
Of course those are not mutually exclusive but it may be worth ranking them. I tend to stress clarity of vision. I know others who stress focus for actions.
Length: As long as you need it to be. 20-30 pages is a good target but if you fall short because you have covered everything you need to, don't sweat it. Some of my early plans were nearly 100 pages.... If you are writing for investors, bankers, etc. 20-30 pages is a harder limit but that takes you outside feelancer territory.
Scope: For a new business, I like to include everything but some people prefer to cover just the first couple years. There is room for disagreement here. The reason to focus on everything is that it gives greater clarity of vision. The reason not to include long-term goals is that it can take away from initial focus on actions. This is your choice. Hopefully the rationales above help you make it.
What to Include
Business plans almost always include:
- A description of the market
- A description of the competition in comparison to what you are doing
- A description of your own products and services
- A marketing plan
- Financial forecasts and targets.
What to exclude
I don't think this is the right question. In general you should exclude material that you find not to be helpful in your business plan. This decision should flow from what you want to get out of the business plan, the intended audience, and so forth.
So this flows from what the focus of the plan is. For example if clarity on the business is primary goal, immediate first steps in the business may not be so important, but if you are trying to focus actions, those may be more important and long-term opportunities less-so.