Content People Want
Now before you say "Duh", this is where many people mess it up. Before they can even get out gate they're destined to fail because they create a product that nobody wants. Sort of defeats purpose.
You don't want to just make money with your product (otherwise, you won't be making money for long), you want to fulfill a want/desire of your customers or satisfy an obsession (aka hobby ;) of theirs. You want to genuinely help them, satisfy their "craving" so to speak.
Having content that people want is number 1 must-have for having a potential best-seller on your hands. (You'll see why I say potential in a minute).
An Online Audience Willing to Buy
Even if you have content that people want, those people have to be online and easily accessible. You're going to be selling a digital book, after all.
People may want latest Harry Potter book offline, but that doesn't necessarily mean they'd be willing to buy an ebook about subject online. Some things just don't do well online.
That's why it's important to test to see if you have an online audience and if that audience is willing to buy what you have to offer. One of easiest ways to do that is to find ezines and forums that reach your target market and survey their subscribers/members. You could have several product ideas in survey and ask their opinion on each.
Go to www.google.com and type in "(target market/niche topic + ezines"). For example, if I wanted to see if there were any ezines for tennis enthusiasts, I'd type in "tennis ezines".
Whoever said not to judge a book by its cover must have said it before Internet was invented. A picture really is worth a thousand words here.
Just like you wouldn't be tempted to buy from a clunky-looking website, so you wouldn't be willing to buy a product with a cheap graphic. (Or would you)?
Either have a professional looking graphic, or don't have a graphic at all. Your sales will only hurt with a poor-looking ebook cover.
Either way, don't kill yourself or waste your time trying to create a graphic if you aren't best artist in world or don't know a lick about web graphic design. Either use a cover template, buy some ecover software, or hire a professional online graphic designer.
Targeted, Unique Bonuses
Why, you ask?
Let's say you sell a product very similar to others in market. With one difference. You don't have a bunch of ebooks that have been around for eons (and that have nothing to do with main product) as bonuses. You have bonuses that you've created (or product by others you've packaged together) yourself.
And if people want your bonuses, then they're going to have to buy through you. You're only person they can get them from!
Unique bonuses can be others' products packaged together in a unique way...
...or, even better, something that you develop yourself.
For example, let's say you have a product a product on ezine publishing. You could take someone else's ebook on interviews with ezine publishers and someone else's ezine publishing software that you have resell/redistribution rights to and make a package that you call Ultimate Ezine Publishing Package, or something like that.
And same principle applies here as it does with creation of your main product--you don't have to create content from scratch.
Or you could do it from scratch and create your own ebook on interviews with ezine publishers or develop your own software (or have it developed for you).
A Home On Web
That includes giving your ebook it's own domain name and a website with reliable web host. It makes your ebook that much more special.
You can get domain names really cheap nowadays. They used to cost you $70/$80 dollars annually, but now you can get them for under $10. Just do a search on Google for "cheap domain registration" or "cheap domain names".
Whichever domain name registration service you use, make sure you have control over your domain name. This allows you to move it to whatever web host you want to, in case you have trouble with any of them.
And with your web hosting service, make sure they provide 24/7 customer support. And that you have at least 99% uptime, web based control panel to make changes to your website in addition to ftp capabilities, access to a secure server license (even if you have to pay extra for it), and email accounts.
Another "Duh" point. No traffic=no people looking at your salespage=no customers or leads. I'll suggest some of usual things you might have heard (or will hear soon enough, if you haven't), because usual does work.
Forget ffa link pages and free classified sites and even safelists. Those things have never worked for me. You'd have to spend weeks, even months, on those before you even see any results. And by results, I mean, one or two hits to your site. You can download my free report Setting Record Straight On Free Advertising for seven dos and don'ts of free promotion online.
Writing articles has worked for me. That's my number one traffic/lead generation method (mainly because it's free...and I like writing). The best thing about having your own ebook is that you won't have to write article from scratch. You could choose an excerpt, or parts of ebook, from your ebook as article, then link to product offer in your resource box.