Learn problem solving. I developed into an engineer very early on by playing with Legos and kinex. These toys taught me analytical skills and problem solving skills at a very early age. Puzzles, chess, mind games.
To be a good engineer, there is a lot of work to put in on math and science. Depending on your interests, there may be more math than science or more science than math but both will be required for sure. To be a "very good" engineer, you need to ensure that your efforts in doing well in math and science are the best they can be...and you need to be open to the idea of learning to write code in some language.
I focus on your term "very good" because there are levels of excellence in this space, just as in any other career. The key, though, is to start small and remain consistent. "Very good" engineers didn't start out that way :). There is a lot of time spent applying what one learns, writing and rewriting code, sharing with others and getting honest, open feedback. To the point about honest, open feedback, it is also important to become a good listener...which isn't something that you can necessarily study but it is something that you can learn.
As your interest grows, you can and should identify areas where you need to develop. Maybe you are interested in doing graphical design or statistics or game development. These are just some examples of spaces where very good engineers spend their time. For sure, when you find your deeper interests, you should study more in these areas to become the "very good" engineer that I know you will become :).
Best of luck to you!
I graduated with a Bachelors in Electrical Engineering. For me, math was most important because it was the most difficult part of the program. If you aren't strong in math it's easy to fix, you need to get extra help outside of class. Talk to your teachers or school counselors if you don't know where to get the extra help. In college I worked with teachers assistants and in study groups to help me on math subjects I couldn't do on my own. Just remember to always ask for help!