i want to write a business plan for a non profit organization which is at start up

The general structure of a business plan does not change regardless of the type of business you are writing a plan for. You should be able to use all the advice and information found right here on Bplans.com to get a pretty good idea of what a business plan looks like and what should be included. I recommend that you start at our “How to write a business plan” page here:
http://articles.bplans.com/writing-a-business-plan

And, of course, check out our library of free sample business plans:
http://www.bplans.com/sample_business_plans.php

If you want personal one-on-one help writing a business plan and you live in the United States, you should find your local Small Business Development Center (SBDC), Business Resource Center or SCORE office to get advice on where to begin. You can check the list on Bplans.com (http://www.bplans.com/business_planning_resources/sbdc/ or http://www.bplans.com/business_planning_resources/score/). Your local Chamber of Commerce office should be able to provide some resources as well.

The success of any business plan is within the quality of the information provided. Once you determine the type of business you want to go into, the plan itself represents the operation on paper as if it already exists: How much revenue is expected, from where, the marketing plans that drive sales, the infrastructure needed to meet the needs of doing business, as well as other related actions and costs. Take your time and talk to as many people as possible for information. Please keep in mind doing your homework up front is like taking on an insurance policy. It increases your chances of succeeding by eliminating the unknowns. In the end there are always other variables.

Good luck with your business!