Definitely agree with the above, research what you want to do. Look at what they can apply to in the civilian world after the fact. I enlisted into a combat position that did not transfer well into the civilian world, and this forced me to retrain once I left the service. It makes you start in your career later in life, and miss much needed experience.
The military can help with education, certification, and housing, among other things while you are in. It can also assist once you are out. Take full advantage so that you benefit fully, and set yourself up later in life .
Prior to enlistment, any college classes can help.. as they can gain you a rank or two (as can eagle scout experience). ROTC is a good thing to check out as well. Going in with a degree opens your options as well.