Whether you've just started your first book or have completed it, don't stop with just the one. Establishing a presence online or in print is crucial and will have readers coming back for more. One way to achieve this goal in a reasonably short amount of time is to break a novel apart into several "books" and they can also be stand alone, but linked. This way, you can publish them all individually and then as a whole. This will increase your sales.
Link your book series together with similarly styled but individually designed covers and they will more than likely also be loaded onto a single page in your Ebook store and be recognized as a series there. When you load up your books, if you put the series title in the title of the book they will be on one page and readers can find them easily.
A continuing character or characters should be established in the first book if you go for a series. This person or couple or group has to change and grow as you write the series, as I did for my lead character in my first book, and thereafter.
Feel free to change your covers if you find that sales are slow or there doesn't seems to be enough attention being paid to your books. There isn't any charge to change the outside or inside on the major online retailer, as well as in their P.O.D. division. As a reminder, in that same major retailer you do have to physically submit separate files to enable readers to Look Inside on the print version posted online. They take care of that automatically with the E version of your book/s.
Lengths may vary of course but a good "short story" or chapter in a linked series is about 5,000 to 6,000 words. This enables you to develop the character or characters and gives a reader the chance to get to know them. You can also have a series of novellas and these should be a minimum of 25,000 words to qualify as long form fiction, because they are true novels.
When you go to load up your Ebooks on this retailer's direct publishing site, there's no need to put a cover jpeg inside of your book as well. They take care of that now so it will save you a step! If yuu create your cover jpeg for your Ebook site, then make it 5x8 inches as this looks great both on the site, plus you can use it for your book's print version, if you choose.