Christian Heilmann lays out seven rules to better unobtrusive JavaScript, including not making assumptions about JavaScript, the browser and the document. Work with structured markup. If you are traversing a document, maybe there's a solution that can take advantage of CSS's selector mechanism instead. Work with browsers and users. Better understanding of events, and playing nice with namespace, scope, and patterns. And of course, think about the next developer, so keep the code maintainable.
Another Douglas Crockford video. This time Douglas talks about the Document Object Model, about how Java failed, and JavaScript evolved thanks to DHTML and DOM. He talks about how to use DOM to traversing and manipulating elements in an HTML document, walking the DOM, making elements, innerHTML, as well as Events, memory leaks. He talks about the cracks in DOM, and how we must be prepared to back off when we hit the browser limits of DOM.