Google displays a double, indented listing when two pages of a site rank on the same results page for a search query. Therefore, whether you or anyone else sees a double listing depends on how many results are set to display. (Change this in your preferences.) If you have your Google SERPS set to show 50 results per page, you’ll see a double listing if two pages rank in the top 50. With 20 results per page, you’ll see a double if two pages rank in the first 20 and so on.

So, set your display preference to 10 results per page. This is what most people who don’t do SEO or SEM for a living have theirs set for and you want to see what they see. After all, what good is a double listing if you’re the only one who sees it? And what good will any double listing do you if it isn’t on the first or maybe the second page?

In order to have a double listing, you obviously have to have two powerful pages well optimized for the same term - or a very close variation of it - or they wouldn’t both rank on the first page. If I were striving for a double listing, I’d begin with a page that already ranked in the top 10. Then, I’d look for a second page that ranked for the same term back in the stacks somewhere.

I’d tweak the optimization of that second page for the desired term - title, description, h tags, text etc. Then, I’d link to it from the page already ranking for that term, using the keyword term as my anchor text. I’d try to build a few more links to the second page, also using good anchor text.

If that worked, then I’d wonder if a triple listing were possible and I’d try for one of those, too!