Pong, snake, even pacman or asteroids – anything of that ballpark complexity, that’s already been made and is familiar to you is a good first project.
Single screen, nothing too complex in terms of game rules, and a well known set of requirements, so you won’t get new features creeping in.
Like Peter said, once you’ve got your basic game done, you can start adding features to it, bringing it new places.
(Other examples: menus, title screen, more gameplay features, better graphics, saving, loading, levels etc).
But be really strict with yourself til you’ve your first version finished.
Have seen people write snake in java as a first non-trivial programming project, and it worked very well from a learning point of view.