Either enlist like above, or do very well in high school and play sports, then go to the Academy for college, do ROTC, or finish college and apply for OTS. Do what makes sense for you. If you dont have interest in being a crew chief or any other enlisted job, then dont go that route. If you do then by all means send it. While it can work, enlisting in a unit is not a fool proof way to snag a slot. There are many roads to take, do some reading on here about the various paths and start navigating down one that makes the most sense to you.