It depends on how short it is and how valuable/specialized the information.
Also if you will be selling it on your site or on Amazon. Then you have to look at the price points that the offer commissions between x and x (sorry, I don't remember off the top of my head) offer 30% commission and the other their is 70% so you want to price it within the 70% range.
Also, you need to figure out "why" you are selling your ebook? If it is short it may be more valuable to offer it for free as a lead generator/list builder if you have other bigger projects/services etc. You would use a different approach if you just want to put something up on amazon as a stand alone, again a different approach if you want o have it as part of a series. You don't provide enough info for anyone to give you really helpful/specific advice.