Remember to target the the sun and do a scan, also you may need to set your Basic Discovery Scanner to a weapon key bind! I think by default it isn't I created a second weapon cycle via the the right control panel in game/ship menu 3rd or 4th tab. Make sure to run that when you jump into a system! Then scan (or not) each planet and sun in the system, you don't need to scan asteroid fields as they do not affect the money you will receive for the scans, even if you do not scan each planet it will still increase your money earned to have a detected them with the Basic Discovery Scanner!
Thought the scanning was automatic... thanks for the info, will put it in practice tonight!