In order to have a fair shot at a good ranking in Google (search engines), you should have the desired keyword(s) in the:
URL (keywords in the actual domain are best, but domain.com/#keyword works)
Page title (meta)
Page description (meta)
- H1/H2 titles
Content (text, alt tags, etc)
###Find the Right Keywords
I’d recommend using the Google Keyword research tool to find the most appropriate and popular keywords you’d like to target. We don’t want just a lot of traffic, we want quality traffic - people who are actually looking for the product/services offered. Pick the BEST keyword(s), just a few, and focus on them.
###Create a section for each keyword
If you have 3 keywords you’d like to show up under, then I’d put them in the page title, description, and create some content sections (with an h1 tag for the title) for each keyword. You’ll basically need to create a section/page for each desired keyword, as you would with a regular site. If possible, make each section have a keyword friendly URL (domain.com/#keyword1, etc).
###Page speed is particularly important
Another aspect is to focus on page speed - the problem with parallax and one page sites is they tend to have really large file sizes - keep the images optimized (ImageOptim is good) and make sure you are using .htaccess rules to speed things up. The last RapidWeaver podcast episode covered this topic really good: Episode 4: Russia connects to you
This can all vary depending on your website and overall goals. As @ashleykaryl mentioned, keywords are ignored for the most part due to abuse.