I don't know any particular magic formula or numbers, but I'd assume you'd want:
- long exposure time / shutter speed to catch a meteor and its trail
- medium ISO so that the momentary meteor will actually register, but not too high (too much noise).
- your aperture wide open (which on the 18-135 is not "that" wide, IIRC), i.e. the smallest "f-stop"
- your focal length / zoom all the way out at 18mm to catch as much of the sky as possible
- Use a sturdy tripod, and a remote if you have one, otherwise use the self-timer shot to give the camera time to stop shaking after you press the shutter to take the shot.
Do these terms / instructions make sense for you? Let us know if not/so and we can discuss this at a level you're comfortable with so you can understand why certain settings do certain things.
Photography is understanding concepts and techniques and then applying them to infinitely variable situations as appropriate; being told what settings to use won't help you get the most out of your camera.
Hope this helps!
