Search Engine Optimization (SEO) is basically a process of making your site very clear and welcoming to search engine robots that will hit your site about every two weeks or so and want to quickly gather information about the page without having to understand or read (parse) the text. Time is money, especially where robots are concerned, and so instead of having to read and understand your site, there are various ways that we have to give them simple information in a way that is digestible to them easily. It pays to give these guys what they want, how they want it.
Luckily, that is easier than it sounds. There are a variety of ways to make your site easily digestible to both humans and robots alike, but the heavy hitters are these 3:
Registering your site on the different search engines. This is a matter of physically navigating to the search engine (google, bing, yahoo, MSN, etc) and performing a series of different registrations on their sites. Some of these registrations will result in those sites generating a piece of code that they want you to insert into the base template of your site.
A base-template is literally a text file with code that tells your website how to build the page in HTML (which is the language your browser reads). Your site will construct that HTML page every time someone navigates to a page of your site. There are some things that remain consistent on each page (like logo, navigation bars, etc) and these are often defined in a 'template' file so that you don't have to redo it every time you make another page. Make sense?
The template file lives on the server of your website host. There are lists of search engines for SEO purposes if you search for them. It is something that could be assigned to anyone under the age of 23 (with specific instructions), and not necessarily something that you NEED to hire a 'professional' for.
Placing 'Meta tags' and 'Descriptions' and other helpful code on your template/pages. This is also generally done on the template, so that you do not have to do it on every page. But it is not rocket science. If you go to a website like: http://www.seochat.com/seo-tools/meta-tag-generator/ you can think about the page yourself, come up with a list of comma-separated keywords, and a description that uses that most common keywords and phrases, and the tool will generate the line of code you need to place between the header tags on your template page. Not rocket science.
My recommendation would be to have a 'brainstorming' meeting (involving creative stimulants like beer) and get a good list of all the keywords and phrases that define your industry. It should not take more than 1/2 hour. Then you want to also draft a description of your site that uses as many of those keywords and phrases as possible.
Once those are written, go to the website above and enter your keywords. Viola! You will have the code you need to submit to your website developer. Remember that in order to insert anything into a template, you will need access to the codebase/server.
Writing the copy of your webpages/homepage. There are all these jargony keywords that are used in the 'industry' (which ever one you are in) that typically writers are taught to avoid using because people turn off when they hear jargon.
HOWEVER, in this instance, computers tend to turn on when you use these jargony terms because they have been taught to look for them. The skill here is to write a page that people will understand and think is interesting while at the same time peppering the text with they industry keywords and phrases so that the computers find it as well.
This takes skill and is worth paying for.
Generally the most important page to focus on is the homepage, but other pages are important as well. If you make changes to the template, they are available for all pages, so the meta-tagging, if done well, can be done once.