I keep a small notebook in my range box that I will record all of my flights at each launch. Just the basics: rocket, motor flown, and altitude if it has an altimeter. Then, when I get home, I have an excel spreadsheet I will update that goes more in depth. For my flights with altimeters, I will include velocity. I will also add any notes regarding the flights, such as if there was damage, or any other interesting events. I will also track the Ns burned, how many motors of each impulse class I have flown, how many times each rocket has flown, I also use it to keep track of my motor inventory and my build pile.