It's pretty similar to article marketing, with the exception being that you have more control over what you include as far as links and promotional stuff. If you want to get sales from Squidoo, your best bet is to optimize your lens based on keyword research and then do a link building campaign. Just building the lens itself isn't usually enough to get it to rank on the first page for keywords that have a decent amount of competition. If you're looking to get on page 1, you have to get some links pointing to your lens.
So in other words, you still have to promote a Squidoo lens, just like you would with any other site.