It's a mobile world, and the same is expected of developers. You cannot always be next to a computer, but you can take steps to help solve a crisis without ruining your day.
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Watching file sizes and following coding standards are only one simple way to optimize your website. Proper HTML will ensure you page is processed as smoothly as possible, but does not mean a major speed boost. When the dust settles from developing a new website, I turn to Google's PageSpeed for the round up of last minute tweaks. PageSpeed alerts you to multiple tips and tricks to help edge off a few milliseconds of your page load - which has become crucial.
Achievements seem to be popping up in every new web service. Why? Because achievements make you win the Internet. Okay, not really, but it does make your user feel more engaged into your web site. It gives the user a reason to use your site and do more things on your site. The best part is the achievements do not even need to be all that difficult. Really the hardest part about implementing an achievement system into your web site is finding a good graphic designer to whip up some images.
When developing web applications it is always wise to use the most up to date APIs and know when to scale back on certain functionality. Google just posted a blog entry stating four mobile web app tips when using Google Maps. Basically it runs down to use API v3, Static API usage, StreetView Images, and JS Map usage.