Search engines crawl the Web looking for pages to list. They evaluate each site and page using a number of criteria based on the content and structure of the pages as well as the number and quality of incoming and out going links, among other things. As a result Search Engine Optimization always requires a multi-pronged approach.
It starts with building the page. Take full advantage of any opportunity to use keywords that are relevant to the page content.
That means making unique, fully descriptive, <TITLE>s for each page, and proper use of <H> tags to mark section topics.
Since it is not possible to include all important keywords in the body text you need to get creative.
Another important place for keywords is <ALT> tags in all graphics. In addition to providing valuable information to visually impaired users, they are also an opportunity to include more searchable content.
Finally you have to get inside the <HEAD> of your page. Google will create the title and snippet it displays in the listings based on page content and <META> information you provide in the <HEAD>. https://support.google.com/webmasters/answer/35624?hl=en
Avoid keyword stuffing (“Foobar, foo bar, foobars, foo bars”) use concise English.
Google, FaceBook and other social networking sites use Open Graph markup in the <HEAD> http://ogp.me/
If you are working in HTML you do this stuff manually. I generally use WordPress and there are plugins to help manage some of this stuff: I like Yoast SEO.
After the site is published you should submit a sitemap to Google’s and Bing’s webmaster tools. If the client has a geographical location you can also create a profile for them on Google Places.
The search engines take the above information to determine the content of your site, but the relevance of the site to any given search is also determined by the results of other searches and aggregate of all the links to and from your site to other sites which have their own relevance (oh what a tangled web we weave).
To boost your rankings make sure that as many sites as possible point to yours. Professional associations, Chambers of Commerce, LinkedIn, suppliers and distributors, friends, FaceBook, etc.
DO NOT be tempted to indulge in comment spamming or other forms of link farming as these will get you blacklisted.
All of the above should be tweaked over time as you observe the performance of your site. You can monitor that performance with tools like Google Analytics and/or tracking plugins for WP, like Counterize.
Or you could get me to do it.