To combat bandwidth constraints, the first thing you should do is apply traditional optimizations which web developers have been using for years: compress the content your server sends with gzip, combine and minify JavaScript to minimize the number of requests the browser has to make to the server, optimize your images, enable the Keep-Alive header, serve assets from a limited number of domains, and use headers to leverage browser caching, among other techniques.
Tip
Optimizing websites in general is a particularly detailed topic, but this section mostly sticks to explaining optimizations specifically for games. If you are interested in learning more about Web Performance Optimization (WPO), start with these rules from Google and Yahoo!:
However, complex games won't be able to rely on browser caching for user return visits because browsers have limits...
