Branding is a simple name for a simple concept with a complex execution: making something recognizable to the consumer as belonging with another thing.
If the food place off the freeway has a funny yellow M standing high on the signpost, we instantly know what price range, type of food, wait time, quality, etc. to expect even if we've never been off this exit (much less in this state) before. If the athletic gear on the rack has a little swoosh on it, the consumer instantly has an expectation of quality, cost, "cool factor", and such. Beyond symbols, owners often try to make memorable taglines. Dixie Plates has trademarked "Strong plates for heavy, messy meals"(tm). These are to differentiate from every other similar product on the market, to try to get a niche that'll attract consumers - in Dixie's case, for people buying plates and contemplating the disaster after a paper plate folded under a helping of Millicent's Death By Fiery Apocalyptic Doom Chili at the potluck.
When it comes to selling stories, we're all trying to connect a few things.
1. Author Name. Seriously, the readers are loyal to the storyteller, and will binge-read if you give them a chance. Readers who loved your last book, put out six months ago, will snap up your new one as soon as you can jog their memory of how much they liked the last one.
We see this as indies, especially when we run a promotion on a single book. Some readers will start on the promo book, and then read systematically through everything else the author has printed, regardless of genre.
2. Series. If you loved the first one, you're going to want to stay with the characters and find out what happens next. If you picked up one in the middle at random, this is how the author makes it clear to you that there are lots more, and the order in which to read for maximum fun.
3. Genre. When you write different things, you will get different fans. Some may love your mystery but not your romance, others love your steampunk but not your literary. This is how you signal to your fan base how to find the other books they particularly want to read.
4. Publishing house / co-op. This one isn't relevant to one-author houses, but the larger your press or co-op of authors gets, the more you want to funnel readers from "I loved this author, I want more" to "This publisher put out great stories, including that author's. What else do they have?" The Big 5 fail spectacularly at this. Baen is a master of this, as is Harlequin.
So, how do we do it, especially as Indies? Several ways.
1. Cover Art.
Look, if your art was awesome enough to catch a random reader's eyes once, stick with a good thing! Use the same artist, or a similar one with a similar style, to catch your reader's eyes again!
Every artist, once they grow beyond imitation, develops their own style. Chandler's "voice" is very different from Tolkein's, and Monet's paintings are very different from H.R. Giger's. If you retain the same artist, your series will be very recognizable by the style of the art. For example. Don Dos santos does urban fantasy, YA scifi, a little fantasy, a little scifi of the more adventure / possibly space opera bent... but you can tell a Dos Santos cover, and you can tell which of the painting in his gallery belong to the same series. Check out his gallery here.
Now, most of us can't afford a Dos Santos, Kurt Miller, Michael Whelan, or Boris Vallejo cover. But you can look at your level. We started with innovari, and when supplies ran low (he hasn't uploaded in 3 years), we went with the closest match in good milscifi ship and art design, PhilCold. (Great artist, easy to work with.) If you have an artist with a unique style that you like and has graced the first in the series from a royalty free site, don't be afraid to contact the artist and ask about a custom cover if you know what you want and they don't have what you need uploaded.
2. Cover design / typography.
If you can't find a similar piece of art, this is where your designer can put photoshop to the test and make a similarly styled picture look like it belongs perfectly - giving it different treatments until it looks like an oil painting, or has decorative moire patterns to match the last cover added in.
The cover designer will also select the typography and kern it correctly - and this is often the most obvious place to build genre and author brand. Go to Amazon and look through some of the most popular series and authors. Note how similar the design of each series title and author can be, and of the author name across their various series.
This, by the way, is why Baen is an instantly recognizable house - it has a limited slate of cover artists whose styles complement, and a single cover designer with an homage-to-pulpy-fun style. (At least, I hear it's only one designer. Even if they have a full team, the lead designer can set the style and tone for everyone under him, and keep all artwork designing to that same principle.)
Note: If you feel that you got the genre cuing wrong or just want a different / better cover, don't feel restricted to the style and fonts of the last cover. You can always use a book launch as a great time to re-brand the older books to match the newest one!
3. Personal Branding.
This is for making yourself a.) instantly recognizable and b.) making sure you leave an impression enough times to be remembered when doing public appearances. John Ringo always wears kilts and has his hair in a ponytail at cons. Howard Tayler always wears formal business wear. Cedar Sanderson has a small collection of evening gowns, while Dave Pascoe can be seen in a kilt, vest, and undone bowtie. (I presume it's tied sometime, but it's always undone when I see him at cons.) David Burkhead is always in black, with a bright purple patch in his dark hair. No matter what your schtick is, be consistent. It'll help fans find you and connect, and let them easily point out so others can go "Oh, that guy!" when you or your books are brought up in conversation.
Caveat One: While mode and manner of dress is a standard way to stand out, it's not the only one - nor does it need to be artificially forced. Calmer Half doesn't have a specific wardrobe, but the distinctive accent, silvery hair, neatly trimmed beard, and dry humour leavened with the occasional war story or pun seem to leave plenty of impression anyway.
Caveat Two: J. L. Curtis - this one's not for you. If you're not doing public appearances, don't worry. And no, blogmeets in the US inbetween popping up in Australia and Italy and points all over doesn't count. Stay safe, my friend.
Caveat Three: when you become visibly branded as An Author, you become a sort of public figure. What you do and how you act in public will become part of your reputation. Generally, being polite and professional will go a long way toward keeping a warm fuzzy feeling toward you. Don't be afraid to hit back when threatened, especially if you can make it as entertaining as Larry Correia, but don't start nothing and think twice before opening your mouth.