G. Mark’s Answer
I'm assuming from the tags that the field you're referring to is "engineer". This encompasses a lot of related areas, such as mechanical, electrical, chemical, petroleum, nuclear, etc., etc.. But I'll simply say "to engineer is human". The drive to solve problems and to be endlessly entertained with playing around with materials and tools and concepts is the key to human advancement and even enjoyment. Some other animals have this same drive and, like us, can't really help themselves but to fulfill it. But other animals don't get the complete buzz we get from basically messing around with our world to suit ourselves.
This is what you do. Keep on doing whatever you're doing, because if you're asking me what you should do to become an engineer, you're most likely already consumed with messing around with stuff to change it into something else you like better. From a house to a car to a soufflé recipe to a quicker way to get to the nearest pizza place, you're always thinking of better ways -- or trickier and amusing ways -- to do stuff.
So you'll be doing related stuff in school, high school, all day outside of school, and eventually apply to college. Then you'l want to decide on what sort of engineering you enjoy. The reason I say enjoy is because, as I've said many times before, people tend to do what they enjoy, they tend to be good at what they enjoy, and they tend to enjoy what they're good at. And don't be afraid to branch out. One fact of success in engineering besides learning the basic concepts is applying them in new ways and in new areas to generate innovation and generally to add to the intellectual property of society to solve problems and make people happy. And this is often by applying principles to solve some problem that actually came from some other area entirely. So the more stuff you know in other areas, the higher your probability is of coming up with cool stuff.
I'd also recommend looking for co-op and internship opportunities and going to job fairs to interact with company representatives. This will give you a much better way of figuring out a good fit and make your career a successful and happy one.