Jill Whalen has written a nice overview of how to get your site ranked well in search engines – Ten Tips to the Top of the Search Engines. In it, she hits all the important points.
To her point #3, I would also recommend Suggestion Tool, Web CEO and Good Keywords as (free) tools that you can use to find the right keywords.
I would say in regard to her point #5, that you might want to put a few words other than your keywords into your Title tag, so that it at least reads in the form of a sentence.
For example, I’m pretty happy with the Title tag on my home page “Professional affordable web design from Smiley Cat Web Design” as it not only gets in my keywords, but also reads nicely on the page and in search result listings.
Never forget that people as well as search engines will be reading your pages, so don’t cater for search engines at the expense of your ‘live’ visitors.
One important point I think Jill left out is to keep your content current. Let’s make that #11:
11. Keep Your Content Current
Search engines prefer sites with content that changes frequently (one of the reasons they love blogs), and so if you want the search engine to spider your site on a more frequent basis it’s important to refresh your content as regularly as possible.
A good way to do this is through some sort of weblog or journal, or a news page (either of your own company and/or the industry you’re in). The most important page to keep current is your home page, so if nothing else you should focus your efforts in this area.