First off, apply to all the academies!! West Point, Navy, Air Farce(not misspelled), Coast Guard and Merchant Marine. Upon graduation, you can select the service that you wish to serve in. Don't narrow your chances on just one. They're all good. If you live in a densely populated state, your chances are slimmer. If you live in Montana, different story.
Religion is also a good addition to a application (alter boy). Boy scouts and or JROTC affiliation is also key.
After you send off your apps (I think before Nov before grad) start inquiring about the military prep schools. Each schools catalog should have information on it. Good luck, Frumby
Attack Pilot
Major USMC