I would have loved the Navy if the entire time was spent at boot camp. No need to think, no need to spend money, and you were to busy to smoke. 
The lack of sleep pretty much sucked, though. No doubt about that.
The real military sucks, IMO. Hope you make friends easily, and have no real politics, or you are going to find yourself with some enemies pretty easily. I was ostracized for befriending someone who was gay. That’s better than the treatment he got, I assure you, but I have my own politics and I couldn’t put them aside. It got me into trouble many times.
Otherwise, the best advice has already been given. Save your money! ALL of your general living expenses are pretty much covered in the military, so there is no reason to not stockpile money and/or pay down debt you’ve already incurred. Banks and such will LOVE to give you loans, and will happily do it only on the condition that you get payments automatically deducted from your paycheck. Forget it. You’re only going to be in 2-4 years. Buy stuff later, when you get out. “It really isn’t that long, and I don’t really need it” – this is your mantra!
There are nice savings plans available to you. Portions of your paychecks can go to buying government bonds, for example, which is really never a bad move. Unless you absolutely positively need to spend your money, save it.
Sure, this sounds simple, but pissing away money on books, phone calls, and nights out adds up easily and quickly. Loneliness loves company and bars/arcades/CDs/you name it. Do not replace companionship with expenses! You’ve been warned by everyone here!

Otherwise, enjoy yourself. Many people manage to, and like all things, it is what you make of it. (hope you went for the college tuition programs they have available!)
If you are fresh out of high school, the military is a PRIMO way to build a fantastic credit rating. Use some money to get a secured credit card. Pick something small like $500 (I don’t think you can get less on a secured card). Use this to purchase stuff and you shouldn’t ever exceed your income. This way you can also pay it off every month (you should be able to as long as you don’t max it out every time, and even if you do you should still be able to pay off a large portion of it every month). You never over-spend yourself this way, and you will have great credit by the time you get out.
I’ve known several people in the AF and they never regretted it. One ended up being a lifer (well, so far, anyway)!
Enjoy your time in! It isn’t hard or easy, but like all things, it is what you make it!