What do you do when you have a web app, rather than content, and there's not that much text to drop your keywords around in. I guess have a blog that talks about your subject matter?
I'm sorry but this is just SO wrong, and the first page SERP's are riddled with low quality examples of why this is not true. I see this regurgitated through-out the blogosphere :\
To answer your question, get backlinks, just get more backlinks. Remember, Google (et al) work off of a link graph, not a "how brilliant is your content" graph ;)
What people NEVER follow up with when regurgitating "just write good content and the rest will follow" is that it's purpose is to bait backlinks, the thought being the better the content, the more backlinks you'll get.
An example: let's say you have a time tracking web app. Your content can talk about good approaches to time management, or techniques to focus, or publish research about the average lengths of different tasks from the data that you can gather from your users.
A great example is Mint.com's blog -- http://www.mint.com/blog/