Projects are the best way to learn in my opinion. Here you will find my favorites. In these projects I've practiced CAD modeling in OnShape and SolidWorks primarily, done a lot of troubleshooting of code and electronics, soldering, programming, and I've learned some engineering mindsets.
I had never done any significant work in python before this project. I used it as an oppertunity to improve my skills and create a cool demo using the Robomaster EP Core Robot. You can find the code on guthub.
https://github.com/Joeshmoe16/DJI-Robomaster.git
I've always been a huge fan of a project by Theo Jansen. https://www.strandbeest.com/ He came up a really clever walking gemetry using genetic algorithims. I created a version to be laser cut using OnShape CAD software. This is far from the first time somone has done a project like this but I had a great time doing it and got a great model out of it. You can access this model in the sources and extras folder.
This summer I put together an electric bike using a kit. My goal was to create a reliable form of transportation to get to my workplace and to work with higher power electrical systems. Using a kit like this is generally straightforward. However I managed to drop the 48v Li-Ion battery, short the terminals, and make a lot more work for myself. I spent some time trying to fix the battery by replacing the battery managment system but ultimatly realized that I had some damaged 18650 cells and a very real fire hazard. While I don't reccomend make a dangerous and costly mistake in a project like this, it was an oppertunity for me to learn to be more careful and patient in my projects.
At the technology showcase I soldered together the 16x16x16 LED Cube Shown Below. It came pre-programmed but the soldering did take 40+ hours.