David Dorward compares dot notation and square bracket notation, where square bracket notation can be used where dot notation can't. Recommends using dot notation, because its easier to read, and square bracket notation when it can't be done with dot notation.
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