Rather than give a lengthy dissertation on web design I have broken it down into following points:

Keep your navigation bars either at top or left of page (a recent tip I heard is: by putting nav bar on right of screen it appears below your site content in html code and therefore will be read by SE spiders last). You can clearly see my navigation bar on left of every page at http://www.007workfromhome.com

Have your navigation bars visible on every page unless its a sales page, in which case you don't want them to go anywhere else.

Divide your navigation bar into related groups of links for easier navigation.

Have you company name and logo in top left or top middle of page.

Keep theme of your site standard throughout. Don't use different fonts on different pages or mix fonts on same page without a good reason for doing so. A constant theme also includes color of unvisited, active and visited links.

Keep your use of colors to no more than about 5-7 different colors per page (less if you can).

Here are some strategies we have personally used with our web design firm:

1) Google AdWords. This is an excellent and cost effective method of getting good search results. You set maximum daily amount you would like to spend on your key words and phrases. Within first month we were getting more client contacts through using AdWords.

2) Overture Keywords. A lot like AdWords, but we found that their system did not really allow you to set a daily limit to how much you wanted to spend and it quickly got out of hand with some of phrases we had chosen! Still, pretty cost effective in grand scheme of things.

3) Yahoo Regional Directories. Once you are able to get your site indexed by Yahoo Regional Directories, I think you stay in there for good! We've been in there for years now and continue to get clients who found us through this directory. (And it is free to submit your site)

4) Keywords / Description / Alt Tags / Title Tags / Page Content. All big SEO companies rely heavily on these 5 things - all of which are contained in code of your web pages. However, with a little research, you could do these yourself (or have it done by your web designer). A few great tools to help you with this task are: Overture Keyword Selector Tool (http://inventory.overture.com/d/searchinventory/suggestion/), Google Suggestion Tool (http://www.google.com/webhp?complete=1&hl=en), Meta Tag Analyzer (http://www.iboost.com/tools/meta_tag_analyzer.htm), and Keyword Density Analyzer (http://www.keyworddensity.com/).

The main benefit to hiring a professional SEO company is that they work for you to constantly update your keywords, etc. and submit your URL to search engines. They know exactly how many of each keyword to use, etc. And this is often a service worth paying for if optimization is a real concern in your industry. A good SEO company will also stay up on what search engines are doing and change their tactics accordingly. They will also never use an "illegal" tactics that could get you banned from search engine. Be wary of companies that "guarantee top 10 placement". I recommend http://www.submitsolutions.com.