If you are new to setting up businesses (even an internet affiliate business with no products of your own, no list of your own). A business plan is a great way to crystalize both to yourself the goals for your business. Even selecting an product to be an affiliate for, It’s very common to just skip this step of market evaluation, competition analysis and then find that you’ve spent hours on a project that couldn’t possible work financially…and that’s really what it’s about!
There are several different ways you can go about generating business plans, from paying somebody $2-$10K to do it (recommend hitting elance for this sort of thing). If you are interested in doing it yourself here are 3 softwares to help:
(buyer beware, read the comments)