People are able to learn clever cognitive strategies through trial and error from small amounts of experience. This is facilitated by people's ability to reflect on their own thinking which is known as metacognition. To examine the effects of deliberate systematic metacognitive reflection on how people learn how to plan, the experimental group was guided to systematically reflect on their decision-making process after every third decision. We found that participants assisted by reflection prompts learned to plan better faster. Moreover, we found that reflection led to immediate improvements in the participants' planning strategies. Our preliminary results do suggest that deliberate metacognitive reflection can help people discover clever cognitive strategies from very small amounts of experience. Understanding the role of reflection in human learning is a promising approach for making reinforcement learning more sample efficient in both humans and machines.