Becoming a missionary is the work of a lifetime. As a missionary, you'll experience the adventure of living in a new area and a new culture, the fulfillment of helping and serving the less fortunate, and the excitement of knowing that you're making a difference. Moving to another country to serve the people there, though, is a big decision, and one that should not be taken lightly. Learn how to pick the kind of mission that is right for you—the one where both you and the people you serve will prosper.
Decide whether you want to give up your modern conveniences. If you must have a flush toilet, going to an out-of-the-way mission might not be for you, and you might want to consider something in a city or a small town. If you are willing to give up things many people take for granted—such as electricity, running water or ease of access to stores and food—you can spread your search to far-flung missions.
Take an inventory of your skills and talents. What kind of things do you like to do? At which hobbies or tasks do you excel? Which languages do you already know, and which languages would you like to learn? Are you good with people? Do you have lots of experience in theology? With construction? Science? Health? If you're a doctor, you might benefit from being in a place where people need medical care. If you're an experienced preacher, you might love being in an area where there are not that many churches and being an evangelist is a priority. Do you like building things? Work with slum dwellers who need your help to construct decent housing.
Go on a short mission trip—one that lasts from a week to a month—with an experienced organization that knows what they are doing and that can shepherd you through some of the initial steps of becoming a missionary. This will further refine the list you started above and give you some real-life experience before you sign up for a longer commitment.
Research and talk to representatives from various missionary organizations that are experienced in sending people abroad for a year or more. These organizations include Maryknoll or the New Tribes Mission, or stem from local churches. Pick the one that makes you feel the most comfortable. Going as a member of a missionary organization or a church puts its resources behind you, and its members can help train you if you don't feel you're experienced enough to preach or spread the Gospel.
Go through whatever training programs are offered by your chosen missionary organizations. They will give you the experience you need to prosper in your new home.
Take care of your affairs at home before you go. Do not leave unanswered debts, mortgages or open financial commitments that you might not be able to meet while you are on your mission trip. Likewise, if you have dependents or children, make sure they are domestically and financially stable before you leave.
Make sure your mind is open! You are about to embark on an adventure that will take you out of your comfort zone. In order to function as a good missionary, you will need to be able to adapt to your new living situations and understand the culture in which you will be working in order to be an effective Christian preacher and worker for God. Likewise, you'll need to confront culture shock, or feelings of shock or disorientation that occur when your new culture does not act quite like your old one.