Business & marketing plans are basic requirements to start a business or revamping a business. These are not static documents, but need to be updated on a regular basis. The SOURCES listed are ones that I felt would best meet the needs of ASU students and the various projects they are required to do. Many of them have step by step instructions. Look at the different sources and see which works best for you.
For those working on ENG 302, you may want to start with the "Starting a Business in Arizona" tab.
Most assignments do not need articles on business plans, but recommended article databases are included for when you do. These also work if you are trying to find a specific company's business or marketing plan, since some articles do talk about the changes in a company's plan or strategy.