Do a real project with goals and expectations. Learn exactly what you need to get the task done. Do not buy a ROS book. Do not spend huge amounts of time exploring the ecosystem. Just focus on making it “do the thing”. The experience will come when the goals are met. Source: I built the entire initial software stack for the FarmBot project (minus the gcode handling firmware, thanks Tim) and had zero hardware experience when I started. I can compile embedded Linux kernels from scratch and whatnot now.