Label your internal text links and clickable image alt attributes (aka alt tags) as clearly and descriptively as possible. Your site visitors and the search engines look at the clickable portion of your links (aka the anchor text) to help them understand what they're going to find once they click through. Don't make them guess what's at the other end with links that say "click here" or other non-descriptive words. Be as descriptive as possible with every text and graphical link on your site. The cool thing about writing your anchor text and alt attributes to be descriptive is that you can almost always describe the page you're pointing to by using its main keyword phrase.
Write compelling copy for the key pages of your site based on your chosen keyword phrases and your target market's needs, and make sure it's copy that the search engines can "see." This is a crucial component to having a successful website. The search engines need to read keyword-rich copy on your pages so they can understand how to classify your site. This copy shouldn't be buried in graphics or hidden in Flash. Write your copy based on your most relevant keyword phrases while also making an emotional connection with your site visitor. (This is where that target audience analysis comes in handy!) Understand that there is no magical number of words per page or number of times to use your phrases in your copy. The important thing is to use your keyword phrases only when and where it makes sense to do so for the real people reading your pages. Simply sticking keyword phrases at the top of the page for no apparent reason isn't going to cut it, and it just looks silly.
Incorporate your keyword phrases into each page's unique Title tag. Title tags are critical because they're given a lot of weight with every search engine. Whatever keyword phrases you've written your copy around should also be used in your Title tag. Remember that the information that you place in this tag is what will show up as the clickable link to your site at the search engines. Make sure that it accurately reflects the content of the page it's on, while also using the keyword phrases people might be using at a search engine to find your stuff.