There's a very useful book called the Sunday Times Business Plan Workbook, by (I think) Colin Barrow - I have used it and won an international business plan competition using it's outline approach, so it is good enough for many purposes. You'll pick it up in WH Smiths, Waterstones, or any other good bookshop. If you're struggling or want further advice, mail me at nhpublic@btopenworld.com.