Search Engine Optimisation is somewhat of a black art. It's all about getting your web pages as high up as possible in the search engine results.
Search engine friendly urls are a big help. Take a look at the address bar whilst browsing this site to see what friendly urls look like.
Meta data such as keywords is mostly ignored these days, it's all about content and what the web crawlers see when they visit your site.
Listing your site on other sites is very useful. Social bookmarking sites like Digg and Del.icio.us can point lots of traffic in your direction and in turn bump up your rankings.