I've been buying and perusing a lot of e-published books recently (both traditionally published and indie published) and scouring the reader/buyer comments. There are two things some indie authors aren't doing that will keep their books from doing as well as they'd do otherwise:
(1) EDITING the Manuscript. This means (a) Spelling/grammar errors and (b) Continuity, redundancy, and storyline errors. This is where you can tell if someone had critique partners. I don't believe your partners have to write in your genre, though I think at least one should. You should have at least two regular partners. Because you need to be prepared to return the favor on critiques and still have time to write! I have one critique partner who writes YA and one who writes fantasy/scifi.
I'll be the first to tell you that getting critiqued is not always fun, and can actually be quite painful. You have to be prepared to hear the good and the bad, to rework the manuscript if it isn't working, and to know when to to go with your own gut. If not for my critique partners, I would have mostly happy reviews from friends and family who love me, and that's not a good idea. It's like working out. No pain, no gain.
(2) FORMATTING for E-Publishing. Amazon, B&N, Smashwords, etc. want you to publish with them, and to that end, they'll all but say you can just throw a word doc or pdf on there and it will work. If you want it to look good, this is NOT TRUE.
I'm extremely lucky in this regard - my husband was a software programmer for years. If you compare my book's formatting to many indie epubs (and I'm sad to say - a few publishing house epubs - WTH?!?), boy can you tell. If an author goes this route and doesn't have personal programming experience or an in-house programmer, they should hire out. It HAS to look professional.
You can't use the excuse - and make no mistake, it is an excuse - that it's "only 99 cents," so it's okay to be sloppily thrown out for public consumption - minimally edited and looking like crap. NO, it's NOT.
Look at it this way: Do you want to build a readership for yourself? Because you can do a lovely job the next time around, and people won't buy it if they've been burned. The idea is to make them look for your next project, not avoid it! Right?
EDIT: In which the Karma Fairy bites me gently, but firmly, in the ass. Reading through the mobi version on my computer , I found one continuity error and one GLARING formatting screwup. Once the file is fixed, it takes up to 5 days to take effect (WTH?), so of course anyone who's already purchased it gets the screwed-up version. So, yeah. Oops. File under: I'm so human and Please don't hate me.