Before I start to go into techniques to help your "online discovery" let's make sure we have our ducks in a row. To that end let's talk a bit about some of the basics for those just starting out.
Priority #1 - Your own site
You MUST have a site controlled by you that you that you can send people to. Period. Don't ever think author pages from: your publisher, Amazon, or Smashwords is "good enough". You must have a site exclusive to yourself that you are in complete and utter control of.
In the past this meant a web page and either learning how to create one or hiring a website designer. Nowadays you don't need any of that just use a blog. Blogs makes it so much easier to update your content and since they now offer static as well as dynamic pages you can still have tabs for things such as sample downloads, buying direct, author bios, contact pages, etc. etc. etc.
The other advantage of using a blog is that you get a SINGLE site. If you try to maintain both a blog and website one will usually be woefully neglected. (Usually the website) If you have only one to keep up to date your life gets a lot easier and you don't confuse your readers by giving them several different places to go to.
What's in a name
While a rose by any other name might small as sweet I want you to start on the right foot and that means thinking about your name (both for your site, and handles used by sites such as twitter and forums).
Writers are in an interesting position because they have their own name, their books name, and in some cases series names. We'll make this real simple because I want you to forget all the other things and focus on YOUR NAME. It's the only thing you can count on.
If you are traditionally published, there's not telling what the "final name" of your book will be. If you stated a blog with the name of that book, and they change the title - you're going to lose a bunch of momentum. Also keep in mind you'll probably have more than one book out there. If you try to make your sites books specific then you'll have to duplicate information on multiple sites with each new book. Also you'll loose cross-selling opportunities.
Some authors think they should divide sites between series. While this is a little better than doing it for books the same problems exist. You'll have to maintain several sites and one is always better. Again if you are using your name as your main site then you can have separate tabs for each series.
What if you write under multiple pen names? I still say you should have only one site. If one of the names is the "Real you" then that should be your site. If all of them are pen names then focus the site on the most popular of the authors then have separate tabs for each of the "writing as" names.
Pay the few dollars a year it takes to purchase your own URL you can even purchase several - for instance yours, your book titles, and your series titles as long as they land back to your one and only blog/website. Through redirection you can have several URL's land at the same place.
Having control over an exclusive place to send people to once you are "discovered" is essential. We'll spend one more blog post on this subject tomorrow indicating what you should have on your site.