As part of teaching self-publishing - more specifically e-Publishing - one of the things I urge is the need to get a book cover lined up before you're ready to publish.
Well, first thing is obviously the book itself needs to be done, edited, corrected, spell-checked, etc. The second thing is the cover.
The book cover is what catches the potential reader's eye. It has to relate to the book's genre or topic. It has to be legible, visible, with a contrast of shadows to light that would not force people to go all cross-eyed glaring at it.
If you're a good graphic designer with effective photo editing tools (Photoshop, cough) then you don't have to worry much. If you're not that good (guilty look here) you ought to go shopping for one.
Depending on the type of book, there are places online you can shop. I've looked at several, tried some pretty expensive artistic ones - had to, for my superhero-themed books - and now I'm looking at the cost-effective ones.
There's a pretty decent marketplace site called Fiverr.
It works like a marketplace where the graphic artist posts their willingness to work on projects for a certain fee. They start as low as $5 - which is a boon for poor struggling self-publishers - and then charge a fee for additional costs. Throw in a tip at the end and you can be getting a book cover costing you around $20. Not too shabby.
An excellent part of the program is the time limit option: you can find graphic artists willing to get this done within a day. Which - if you're pressed for time focusing on a looming release date - can help get at least one thing taken care of while waiting on the rest.
Just to note, I did hire someone on Fiverr name of leahdesign, and she did good work so if anyone else is looking, check with her.
Good luck with your writings, everybody. And don't forget, NaNo is almost one month away!