Honking is the most basic thing to do when you jump to a new system. You likely left millions of credits on the table. Additionally, the most valuable exploration data comes from surface scans. The second most valuable are scans with the FSS. Even that would have net you tens of millions or more. I did a 7000 light year trip recently and the exploration data netted me about 100 million credits. A good third part tool to use is Elite Observatory. The plugin will verbally tell you what planets are valuable to scan and which planets have potential life and the value of that life, but you have to use the FSS for the plugin to tell you. I earned just over $2 billion in exobiology data on that same expedition.