Search engines like Google have two purposes; making sense of the web, which they do with crawlers, and prioritizing the best websites to navigate users to relevant and quality content. Having a well-structured, consistent and simplified website with quality content can make the difference between being at the top of the list or at the bottom.
My rule of thumb is build a site for a user not a spider.
~ Dave Naylor
Crawlers only see written content on your website, currently. They jump between the links on your website and make sense of the tree of pages. It is important not to have duplicate pages or the crawlers will identify your site negatively. They scan through the pages and capture and prioritize your site based on URLs, tags, and content.
Organize your code using proper tags. Some of the common tags to use are Title, Meta and Heading tags. A Title tag tells both the user and crawler what the current page covers. It should be unique to each page. Make these tags brief, specific and clear. It will be easier to find. The Title tag also contains the content that will appear on the search engine description.
Meta tags summarize each page in more detail. The same rules apply as the title tag except for length. You can go into more detail when writing a Meta tag.
Heading tags are used to emphasize important content. The crawler will use these to prioritize content to make sense of. They are also useful visual cues for your users to make sense of what to read first.
Alt tags should be used on images to help screen readers describe your images. Make sure you descriptions are clear and specific.
Make sure your site is easy to navigate and the page structure makes sense. Organize your code into a folder structure that makes sense. Navigation is very important for crawlers because it helps visitors find the content they want. You can use tools like breadcrumbs, if your site is complex, to let users know where they're at within your site. Using clear and concise names for your folders and pages will ensure users easily understand your site, unless you're worried about security. Finally, what happens if a user deletes part of a URL. Is your site ready to handle a 404 error. Make sure you have a page setup for this reason.
Creating useful content will move your website up the ladder. Users know good content when they see and they will probably link other users to it. Think about what users are looking for to find your content. Someone who is an expert in your content topic may search something very different than someone new. Make sure you know your audience and which users you're trying to reach. Consider using fresh, unique and exclusive content to stand out from other sites. Your site will stand out if you have quality content.
Refer to Moz's resources to learn more about SEO:
MOZ SEO Guideline - Learn the ins-and-outs of search engine optimization.
MozBar - Provides easy access to SEO tools and data while you surf the web.