If you are interested in working on cars, gain a good understanding about how a car works. This may mean driving and getting under the hood of new and older cars as they operate differently. Do you know what a U-joint is and what it is for? How about a master cylinder and its function?
Many of the cars today rely on electronics. Learning about the different parts how they interact with each other will increase your knowledge and give you a holistic view about how a car operates. This will be beneficial when troubleshooting. Having an understanding about how things fundamentally work can be transferred when on other projects such as home and equipment repairs.
Good luck to you!