It sounds obvious, but take a lot of science and math classes in high school, at the highest levels you can. All engineering programs require some physics classes, usually before you can start taking your real engineering classes, at the college level - and those physics classes use/require calculus. So if you can have some experience with calculus before starting college, that's a nice advantage (if not, don't worry - lots of engineers have to take calculus in college anyhow). Same with physics/chemistry.
Also think about taking some programming classes. Even though you're not looking at computer science, some programming knowledge can be helpful or even necessary for any type of engineering. This is something you can start learning on your own, too. Lots of tutorial websites and books exist for most programming languages. A pretty nice and easy one is Python.
Focusing on the SAT is fine for getting in to colleges, but that's about all it's good for - really knowing the SAT isn't going to make you succeed in your college classes or be a good engineer. Keep that in mind when studying for it.
Another piece of advice - spend some time doing hands-on experiments. You can get an intuitive grasp of how things work that will help a lot in college. As an example, maybe try some of these: http://missionscience.nasa.gov/scientist/experiments.html Going off of the rocket project there, here's an example of an engineering project.
Build the rocket they have on that page (or another, doesn't have to be NASA) and set some goals. As an example, you might say that you want the rocket to travel at least 50 feet in the air, open a parachute, and land safely. In order to meet the goals, you'll need to learn some other things first - how to tell how high a rocket is from the ground, what makes a rocket have a nice stable flight so it's spending its energy on flying up instead of to the side, that sort of thing. Once you've learned those, you'll have to make decisions about what you can make - if you could use carbon fiber it might go 100 feet up and it's strong so it can handle a rough landing, but it's much more expensive than cardboard, but cardboard might not be as stable so it won't go as high or it might not survive without a good parachute, and so on. You'll have to make decisions about things like that - can you meet your goal using cheap cardboard, or do you have to use something more expensive like PVC pipe? Then build it and test it. If it doesn't meet what you wanted it to do, figure out why and try to improve on it. THAT is what engineering is.