What makes a good investor, is simple the ability to understand the risk and plan very well before making any move. Having patience also can make one a good investor as investment take time to yield good result. If one is not patient, he ends up investment in the wrong time and making rash decision that can complicate his  investment .
As some good strategist has said before now, always learn to diversify portfolio and avoid placing all eggs in one basket. As this is another way to be a good investor. Learn new strategies, follow new trends, always be informed about latest Change in the market and overall, take you time to plan. Don't be in a hurry.(fomo) and with  these you  can become a good investor.