In the long run, your data matters more than your code. It's worth investing some effort to keep your data in good shape for years to come. Data is at the heart of science. A scientist is expected to be able to back up all published conclusions with data. Data management should thus be a priority in science. Scientists can't afford to lose data, be uncertain of what it means, or not know where it came from. In the experimental sciences, there's a long tradition of writing down all experimental setups, parameters, and results meticulously in a lab notebook. Unfortunately, computational science is much less rigorous about data handling, although there are clear signs of improvement. Here, we'll consider what you can do to better prepare and manage your data.