Use a good sturdy tripod, disable image stabilization, use manual focus. If you shoot RAW you will need to increase "black" in your processor to reduce "Noise" Also use either the timer or a remote shutter release to avoid camera shake which creates a blurred image. You will have to experiment with ISO's, & shutter speed. Remember: if you use a wide open F-stop you will get light quicker which will mean you need to reduce your ISO or increase shutter speed. Towards F-22 the opposite will be true, you may get better focus with a small aperture but the exposure may take long enough that you may get a blurred image due to the earth's & planet movement.
