In working with both web designers and search engine optimizers, one thing I've noticed is this: They're often at odds with each other. It's unfortunate that too many web designers think SEO is snake oil (or evil, or unethical -- whatever you want to call it) and many SEO "experts" have no clue about design.
Thousands of SEO companies around the world aggressively, or not-so-aggressively, follow the SEO principles they read on the web. But when it comes to decisions that affect usability, readability, aesthetics, and the simple functioning of a website, they're either innocently ignorant or willfully so to accommodate their SEO principles.
Look around. Some of the best and genuinely helpful SEO companies have the finest website designs. Read their HTML source code. It has all the genes of properly SEO-formatted code, yet the whole thing works like a charm. It's a win-win: users get to explore a website that is both good-looking and "good working." And Google can easily index the site and assumes everything is fine.
That's the golden mean you want to achieve if you really hope to win both the users and Google. After all, there's little point in getting to the top of Google rankings if you don't have a user-friendly site.
All Roads Lead to Usability
Usability is what matters most. Is your site pleasing? Is the content clear? Is it formatted so as to present friendly, readable, and distraction-free content?
Do ads block your way around the website? Have you cloaked any links or text? Is the navigation simple and clear? And most importantly, can you get to read the content immediately or do you have to scroll through a maze before getting to the meat of your site?
Hardcore SEO technicians (who aren't fully professional, really) will probably frown when you tell them these issues matter in SEO. After all, usability can be overlooked when SEO concerns come to the fore, right?
No, it can't.
Google wants your website to be as user-friendly as possible. This is evidenced by recent algorithm updates like Google's Above the Fold update which detects whether your website has more than two/three ad slots above the fold. Even Google's Panda algorithm update was designed to detect and weed out websites that provide a poor user experience.
Google isn't all that smart but it's getting there. And if you think of Google as a user, you are on the right track to making things great for yourself as well as for the reader.
The Basics
1. Watch Your HTML
Semantically correct HTML is what your website should feature. If you rely on a blogging platform like WordPress, make sure you get the latest version and upgrade as often as you're advised to. It's HTML5 that's ruling the roost now, but if you are using HTML 4.1, make sure your doctype is set to the correct parameters.
People usually don't emphasize the usage of correct, non-deprecated tags, because from an SEO point of view, that doesn't really matter. There was an incident when someone pointed out that Google was still ranking the old "bold" tag over "strong" and everyone jumped ship... only to find out much later that Google had mended its ways soon after that.
Make sure you/your SEO expert/content editor doesn't use deprecated tags. In the world of HTML, Google isn't leading the batch. In fact, Google follows the conventions, so make sure you use the up-to-date version of HTML and the tags.
2. Author Bio
Rich Snippets and Google+ authorship are playing one of the most vital roles in SEO today. It's a strategic thing that Google is using to measure Author Rank and verify authorship. The basic underlying principle is to apply a personal face to a brand that uses content to market its services. Simple, genuine, and truthful.
If you run a blog on a WordPress-style platform, you should make sure your author profile is set up properly. Use a full name that matches the one on your Google+ profile.
If you are using a custom platform for your website/blog, you need to make sure the posts have properly formatted authorship information: something Google can pick up, decode, and read easily.
3. HTML Sitemaps
This item should require absolutely no introduction. Google prefers HTML sitemaps to XML, so ensure you have an HTML sitemap. Since you're going to be creating HTML sitemaps, make them easily "navigatable;" this improves the user experience.
4. Use Aesthetically Pleasing Images
Many SEO professionals use images in their content because someone told them that using images "attracts readers." Other than relevant images that may or may not be aesthetically pleasing (you're most likely not going to drool over a screenshot of Google SERP), if you are using an image as, say, the title graphic for a post, it should be "enticing."
Some of the real experts shell out a lot of money just to create graphics that are relevant and enticing.
Images are indexed by Google, of course, so be sure to include specific title and alt tags. However, don't stuff them with keywords. Just as you want your content to flow naturally, your images should have meta data that are relevant and explanatory... not keyword-stuffed.
5. Meta and Titles
Speaking of which, that brings us to the meta debate. Should you focus on meta descriptions? Are meta keywords no longer necessary? Should you write keyword-based titles, or should you just forget about keywords and focus on enticing titles?
This is really an issue of content rather than design, but it's your front-end designer who's going to write that piece of code, so it's probably better if you make this decision.
The answer to all the questions above is yes... and no. It depends on what kind of approach you are taking. If you are the plain old SEO guy who isn't aware of Google's content requirements, you'd probably go with keyword-rich titles, keyword meta tags, and descriptions. Don't get me wrong: keywords in title still do matter, but only when it's natural, or you are already an authority with high ranking.
The meta keywords tag, however, is no longer a part of the technical jargon in SEO. There's not much harm in having it (except for your competitors easily discovering what your target keywords are), but almost certainly no benefit, either. As far as the meta descriptions are concerned, you should include them, and write them in a way that makes people want to click through to your site. After all, this is the snippet that Google is probably going to display in the search results.
6. WordPress Plugins
Webmasters who use WordPress are often at an advantage over those who don't. WordPress comes with a ton of SEO plugins that make it easy to run a checklist of SEO functions on all your posts. But when you do get to use them, make sure those plugins aren't having an adverse impact on your website, either directly or indirectly. I've seen people use just a couple of plugins for SEO, but they ended up ruining the website's load times, performance, and ultimately, usability.
To say that we've just scratched the surface would be an understatement. There are tons of other issues you should take note of -- like title tags, exact-match-domains, page load times, navigation... not to mention mobile/responsive web design.
Overwhelming as it all sounds, there's really just one thing you need to remember: usability takes precedence, because in the long run, Google's future algorithmss are going to be trying to weigh quality, and reader experience is paramount.