This gotta come up with a project you want for yourself and make it. I remember soldering one of those 2x16 LCD screens and it had a short so it would start smoking to designing/3D printing my own quadruped with an IMU/navigation. I did cheat and not use inverse kinematics, I watched videos on other insect-style quads walking and I programmed it manually.

I think main gotcha is power distribution and shared ground eg. using a boost converter or regulator to boost/downgrade voltage and which servos/sensors uses what. Later have to be concerned with too much current being drawn but yeah.

I used these green proto boards you can solder onto as a step up above breadboard but not my own PCB.