I'm working on a project to improve student engagement in my classroom using psychological principles, but I'm unsure about the practical differences between positive reinforcement and negative reinforcement. How do I decide which to use effectively?

I've been studying basic psychology to apply it in my teaching role, focusing on behavior modification techniques. I understand that both positive and negative reinforcement aim to increase desired behaviors, but in real scenarios, like managing a class of 30 students with varying motivations, I'm finding it tricky. I've tried using praise (positive) and removing a minor privilege for off-task behavior (negative), but the results are mixed. What's a systematic approach to choose and implement these reinforcements without causing unintended side effects?