By way of a coda to my previous post about the power of the backlist, I should mention that it can be something of a double-edged sword. The power of the backlist can cut both ways.
It is true that the backlist can work in your favour–that when you have multiple titles, then for every book you sell, at least a subset of those readers will buy your other books. But tempting though it is, don’t rush out and publish all your back-drawer, barely-edited manuscripts just yet, because the readers who come back will do so because they enjoyed your first book. You have to make sure the other books you put up are of similar quality and are in a similar style.
I have another half-dozen romance manuscripts sitting around. I haven’t put them up because I haven’t had a chance to look them over. They will likely need work, and I don’t have time for that right now. So they’re sitting on my hard drive, and will continue to sit there until I’ve vetted them closely and determined whether they’re worth editing, reworking and polishing in anticipation of putting them up. I count it a real honour that readers have come back for more, after reading my first book. I don’t want to screw that up.
Basically, your books have to be as good as each other (allowing for growth as a writer etc., which will see improvement across titles. This kind of shift is understandable. I’m just saying, do your best with each book–don’t just throw up something that’s half-developed or not really ready for wider consumption, just in order to have a backlist). Otherwise, whatever goodwill you build up with a reader, thanks to a first title that they enjoyed, will be dispersed if they find that your second title is inconsistent with the first (not as well-developed, etc.). Each comparably good book will reinforce the previous, positive impression, and each sub-standard one will erode that goodwill. Wisdom for the ages, friends. Wisdom for the ages.