There are some situations where debugging your Android app on emulator isn't enough. Maybe you need to test some native code (gamedev?) or just want to test some performance critical UI elements. There is a standard way to do it by USB cable and ADB. But there is more convenient way to do it.
When you have rooted phone you can do it over your WiFi network. There is a super easy way to set it up in eclipse environment. First, install ADB Connect plug-in on your Eclipse instance. The easiest way is to do it by Eclipse's internal update mechanism. Go to Help-->Install new software and add this source to the Location field: http://ppareit.github.com/AdbConnect/
this app on your phone. IT WILL ONLY WORK ON ROOTED PHONES! Start adbWireless when connected to your WiFi network. Click Window-->Preferences in Eclipse. Type adb in filter text filed, and set up your IP and Port number from adbWireless on your phone. Apply changes and click "OK".
Now hit new icon on your Eclipse's toolbar (the one with Android mascot's head and "wireless" symbol). There might pop up some error message, click "OK" and don't worry about it. If the icon stays red, you probably have connection. Run your app as usual, if your minSdkVersion is equal or smaller than your phone's Android version, app should run just fine. You can test it on your phone with full feedback (DDMS, Debug mode, LogCat).