Using HTTP Injector can be a bit complicated, but its official webpage has a very handy manual to help you out. Plus you can import the configurations created by other users, and it takes just a few seconds to do so.
Within HTTP Injector there's also a wide array of different tools. The IP Hunter, for example, lets you look for local IPs, while the diagnostic tool gives you the chance to check that everything is running properly on your device.
Requires Android 4.0.3 or higher.