Here, I'm pasting what they say about Foreign Service Exam. This is right up your alley. It's like they're talking to YOU.
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The Process Step One: Research the U.S. Foreign Service.

The Foreign Service isn’t your normal 9-5 job. Even if your duties aren’t anything crazy (though they probably will be), you’ll be doing the work in Romania or Qatar or China or Papua New Guinea. It is important to have an honest discussion with yourself, your loved ones, and your Golden Retriever Kissinger. Are you ready for the massive disturbance in your life? Not just uprooting and leaving everything behind once, but constantly, every two or three years? Do whatever you need to do. Make a pro and con list. Talk to people who have lived overseas, even if they weren’t diplomats. Network online with other interested applicants. Most important, be honest with yourself.

Step Two: Don’t Research Too Much.

You’ve done Step One? Good. Now just take a deep breath and don’t fret so much. It is free to take the Foreign Service Officer exam (unlike the hundreds of dollars you have to dish out for the GRE, MCAT, LSAT, and countless other tests.) Take the test on a whim if you want. The Foreign Service isn’t the military. It definitely isn’t the French Foreign Legion (even if your Aunt Ruth will never figure that out.) The Department of State isn’t going to draft you just because you take the test. If you take it, and change your mind. You don’t have to join.

Step Three: Go to Careers.State.Gov

Click that link up there and look at all the steps involved. Don’t be daunted, but take it as a reality check. No matter how awesome you are and how great you do on the test(s), this process takes time. From when you pass the Foreign Service Officer Test to when you join a class (known as A-100), it will be at least six months, probably closer to a year. The Department of State says the first step it to select a career track. We’ll go more into that later. While it is a big decision and should be thought about at this stage, don’t stress too much. It is untrue that you cannot change it later, though it is difficult. Look at the tracks and go with your gut. If you’ve spent years doing management work, but you really want to work in public diplomacy, go with public diplomacy if that will make you happy. Doing a job you didn’t like doing in Omaha will not be any better in Rome.

Step Four: Register for the FSOT

It isn’t offered continuously, just a few times a year. It is still better than the once a year it used to be offered. Why is that better? One, because if you decide in February you want to do it and the test is only offered in January, that is a long time to wait. Two, if you fail the test, you potentially don’t have to wait as long to re-take (you do have to wait though.)

Step Five: Get to ForeignServiceTest.com - See more at: LINK