What I would do -- what I actually do do, as a matter of fact -- is dive right in and learn on the go.
Necessity is the mother of invention -- or, in our case, the mother of resourcefulness. I.e. nothing will make you learn something faster, and better, than having your website crash/not-work if that particular something isn't done right.
That being said, don't go overboard; or be overconfident. Do practice the basics, before diving head first into your new website/app. And by "the basics" I mean getting a website up and running.
Then, you take that and you run with it -- as fast and for as long as you can. There; that's the secret to startups, right there :)