Ask HN: What are "correct development & programming practices" for a web app?

I am learning Ruby and Rails now, and this thread - http://news.ycombinator.com/item?id=909048 - made me start thinking about what 'correct development & programming practices' are for a startup.<p>Can someone provide some details about specific things that you would implement, if you were creating a startup from scratch (i.e. building a web app).<p>E.g. I know obviously having and using some VCS, and implementing unit tests, but other than that....what else would I want to make sure to know/do?<p>Thanks.