Star trails make the best first step for beginners. You will learn all you need to understand to get started in astrophotography but you are less impacted by things like: the time of year, light pollution, the moon phase.
Star trails can be captured at any time of the year, under any moon phase, and you are less required to find dark sky sites.
Therefore you can go through all the steps and end up with an amazing photo and have learned all you need to get started in astrophotography.