Select a subject that has a big market of motivated people.
Like: weight loss, stop smoking, ways to make money, etc.
Search for affiliate programs on Google in that category and
at the Affiliate Networks like CJ.com, ShareaSale.com, etc.
Write useful articles on the subject and submit them to sites
that get a lot of traffic and that Google favors like Squidoo,
Blogger and EzineArticles.com
Write a nice resource box for your articles recommending readers
visit the site who's product you're selling. Use your Affiliate link
as the url.
Take each article you write and use it to build your own website
as well.
You'll find a lot more good stuff on this at
http://www.terrydean.org