Although Christian Heilmann covers what he wished he knew about JavaScript earlier, he actually points out the features JavaScript developers should know: shortcut notations, JSON, native JavaScript functions, event delegation, anonymous functions and the module pattern, allowing configuration, and using good libraries to abstract away browser differences.
The Yahoo! Web Developer Network provides a one page overview of JSON, giving a quick tutorial on JSON, how to get Yahoo! Web services to emit JSON, offering an output of a JSON object literal as well as using a callback function method. Yahoo! also describes how their web services typically translate their XML structures into JSON.
Ryan Campbell of Particletree offers a step-by-step guide to getting started with JSON. Since JavaScript can use JSON to either send or receive from the server (both parts of an AJAX request), Ryan suggests getting started with sending JSON (after stringifying it) to the server and converting it to a server side object. Then sending that object back, encoded as JSON, to the client and process that. He offers working library code for both JavaScript and PHP (for the server part).
Douglas Crockford's presentation on Advanced JavaScript. He covers topics such as inheritance, modules, debugging, efficiency and JSON.
Matt Kruse's JavaScript Toolbox presents a number of excellent best practice ideas including: using var, feature detection, when to use square bracket notation, avoiding eval, referencing forms and form elements, avoiding the with keyword, using onclick instead of JavaScript pseudo-protocol, using unary + to type convert to numbers, avoiding document.all, not using HTML comments in script blocks, avoid cluttering the global namespace, avoiding prototype.js, avoiding synch Ajax calls, using JSON and the correct way to use script tags
Douglas Crockford introduces the JavaScript Object Notation, a lightweight data interchange format that's giving XML-based web services a run for its money. Its a subset of the JavaScript programming language, and very easy for programs to parse or generate, and so its not surprising that all major languages now have JSON libraries/code snippets.