Before entering the military make sure you know what you are getting yourself into. Too many people join the military without thinking it though and end up regretting their decision. Once you join your stuck until the end of your enlistment. If you get out any earlier for one reason or another you will not get an honorable discharge making it next to impossible to find a job that doesn't include fliping burgers.
No matter how sure you are about joining the military it is almost always better to just go to college. The military is good and all but it's like takeing the easy way out. The military makes all of your life choices for you, how you spend your time, where you live, and sometimes even how to think. If you go to college you have a chance to make something with your life. While in the military you are stuck doing what they tell you.
Of course you can't talk about college without mentioning the Post 9/11 GI bill. If you joined the military after the September 11th attack then you are eligible. The GI bill pays 100% tuition, books, fines and even pays you BAH for a E-5 with dependant rate (Basic Allownace for Housing varies from place to place but generally is about $1000 a month.)
You also get 100% tuition assistance while you are enrolled in military service. If you plan on taking college while still on active duty then make to pick the right job. Many jobs in the military demand too much time to make it feasible to attend classes while in the military.
#2 Guard and reserve
Most people don't realize that each branch of service has its own guard and reserve units per each state. There guard and reserve offers the same benefits as active duty if not more. Many people are turned off to: 1 weekend a month 2 weeks a year. What they don't know is that you can get hired to do the same job you do for the guard, but you're considered a civilian and get more money and actually get overtime pay. Also, they deploy just as often as active duty.
If you are planning on going to college while in the military Guard/Reserve is best choise.
If you join the guard or reserve your life will be much easier than it would if you went active. They are more relaxed in every detail: uniform standards, amount of work, standards for promotion. I once went on a temporary duty to Nellis AFB along side a guard unit and they just sat around chilling in some lawn chairs they brought with them most of the time.
Many people join the military without even realizing that there is two types of rank, enlisted and officers. Officer is basically the white color worker and enlisted is the blue. This being said, officers make over twice as much money as enlisted. You have to have a bachelors degree to apply for the officer program but it doesn't really matter what your degree is in (I've seen plenty of fighter pilots with education degrees.)
Many people join as enlisted thinking they are going to get their degree and switch over to officer. While this can be done it is very hard to pull off. Even if you can get your bachelors degree, about 90% of enlisted-to-officer requests fail. The military likes to train fresh officers without bad habits; if you want to cross over, your personal file better be outstanding and even then you'll probably fail your first few times making the request.
#4 Research the Job You Want
The military is very hit or miss as far as jobs go (same thing for what base your stationed at.) You're pretty much either going to get hooked up or get screwed, not much room in between. Don't select a job until you know what you're getting yourself into, your recruiter isn't going to give you a chance to re-select if you change your mind. After you select your job, do a little research on-line to get a general idea.
Also don't go choose Open General because they don't select a random job for you, they give you a jobs nobody else wants like security forces or services.
Find someone in the military (not a recruiter, they never tell the whole truth) and ask them about the job you want. If you can't find someone in that job at least make sure their in the same branch of service and they should at least know if it's a good job or not. I can answer any Air Force questions you may have in the comment section (I was an F-15 Avionics Specialist.)
#5 Which Branch of Service is Best?
I'll admit right away that I'm a little biased toward the Air Force but all the branches have their individual perks. The Air Force is arguably the best to join overall. The AF has the best living conditions, deploys the least, has to put up with the least BS, and is the most exclusive branch. Also, they are the least likely to call you back into service on your inactive reserve after your enlistment is over.
The Navy is pretty comparable to the Air Force. All of the conditions I listed for the AF above pretty much apply to the Navy. Plus, you get to be a "seaman" which they changed from "sailor" because they said it was less homosexual, no joke.
The Marines is the best branch to be a solider. They have the most prestige out of all the branches. The marines don't have to put up with as much BS as the army and they don't deploy for as long either.
The Army is the easiest to get into, they are the only branch that is constantly undermanned while the others are downsizing. With this, they offer the best sign on bonuses as well as the fastest promotions.