i want to start a video production company, how do i write the business plan?

Check out the answer to these questions:

http://www.bplans.com/ask-bplans/2668/have-grapes-growing-dont-know-write-business-plan-proposal

http://www.bplans.com/ask-bplans/2460/how-write-good-business-plan-sawdust-briquette-production

There are a number of similar questions that have been answered, and as mentioned in many of the answers, regardless of the type of business you are going into, the process of planning and writing a plan is the same.

Good luck.