A foundation for Engineering is a competency in math, including algebra, geometry, trigonometry and calculus.
Other skills that I consider important include: problem solving, deconstructing systems of all types into component parts, communication, sciences (especially physics plus chemistry), curiosity, ability to focus and lateral thinking.
LMK if you want me to expand on any of the above.
The other folks already included problem solving skills and other "hard" skills one needs to be an engineer. There are other "soft" skills needed to be truly an effective engineer: leadership/ teamwork/ effective communication. One of the ways to learn those skills is by watching others around you have demonstrate those skills well, and either follow their example or just directly ask them "I noticed that you are a good communicator/leader in these situations, I'm trying to work on those skills, can you share with me a few tips?"
I think the most important mindset in order to become an engineer is to have the curiosity to wonder how things work. Whether it is wondering how cars function, how that video game of yours works in so many user interface layers, or wondering how a bridge can support all the weight it has, these are all marvels of engineers. As engineers, you will one day solve existing problems or improve some sort of product/process through the combination of math, logic, applied science, and some creativity. The ability to "think outside the box" cannot be said enough. Good luck!