Gaining superuser access to your phone is just the first step in a vast new territory of Android exploration. Depending on which rooting app you're using, you may already be enjoying the performance and usability benefits of a host of enhancements included in your root recovery image. But there's plenty more to explore.
If your phone doesn't support Wi-Fi tethering out of the box, you can now add it to your rooted phone. Barnacle is a good, fairly simple app that exploits root for tethering with or without your carrier's support.
Root users also have the option to overclock the phone's CPU to give it a serious performance boost. For this task, it's hard to beat SetCPU, which offers a friendly slider-bar interface for setting your phone's clock speed. But be careful: Setting your clock speed too high can damage your phone permanently.
The ultimate Android hack is to replace your phone's default operating system with a custom ROM. You have many to choose from, and each has its own pros and cons. Some ROMs are designed for specific phone models, and not all Android phones support the installation of a custom ROM. As of this writing, the Droid X is particularly problematic in this regard, while handsets such as the Nexus One and Droid Incredible support a wide variety of ROMs. The best way to find, install, and manage ROMs is to run ROM Manager, which is available for free from the Android Market. ROM Manager Premium even offers a large list of available ROMs that you can download straight from the app itself.
By now you should have a pretty good handle on working with a rooted Android device. I've attempted to cover all the basics in this guide, but there's no shortage of additional tips, tricks, and advice that can help you improve how Android functions. If you have some tips of your own to share, please chime in with a comment. And if you think my attempt to simplify the process has resulted in a significant error or omission, please let me know by e-mailing firstname.lastname@example.org.