Before you begin writing any mini E-Book, it is important to research the demand for your chosen niche. If you write a book that no one wants to read, it really doesn't matter how powerful your marketing efforts are.
When you research the demand for your chosen niche, you can use a number of different avenues. One of the most straight-forward includes looking at aggregate data. You can do this by searching for your chosen niche at the following URL: http://inventory.overture.com. This will return a list of keywords, along with aggregate search data, which loosely translates into demand.
Another way in which you can research the demand for your chosen niche is by browsing forums. This seems highly anecdotal, but it isn't. If you want to produce products that are inline with current demand, you will also want to understand your current customers. One way to do this is by looking for hot topics on forums. If people are ceaselessly complaining about something in your niche – and you can provide the exact solution they want through a mini E-Book – why not do it?
Another way in which you can research the demand for your chosen niche is through online surveys. Purchase some pay-per-click traffic and send it to a page with a poll about your given niche. Find out exactly what people want most.
Additionally, if you have a list, the best way in which you can research the demand for your chosen niche should involve sending out a mailing that asks your subscribers for input. If they all want the same exact thing, then give it to them in the form of a mini E-Book. Unless you have a good reason not to do this, this is an excellent way to take advantage of existing demand in your niche to make some product sales.