Sketching in Code by A List Apart.
I'm a big believer in massively iterating. Start small, show people what you got, and improve. Rince and repeat.
Make sure you use a source control management tool like git, and tag the code each time you get something working, so that if you don't like the direction you went in the last couple hours (or days), you can just zip back to a previous version that worked.
I also like to do this with one host that I look at things on, and then push out the latest version to another server, so that your users can always see the latest good version, and not see your current working copy.
