This is a good and important question. If you want to be an intercultural missionary, then you should take some concrete steps.
First, you may want to attend seminary. During seminary, you will learn theology, counseling, and history. While all of these courses are important, any course on the history of missions or contextualization will be important. This will help you see what others have done before.
Second, you should do some research about what country you would like to go to. You should familiarize yourself with the differences in culture and most importantly start learning the the language. This alone will take a lot of time.
Third, you should also try to spend some time overseas. Without some exposure to a different culture, you will not know if you really want to go.
Fourth, start getting in touch with missionary agencies. There are many of them. Also most denominations have foreign mission departments as well.
Finally, find a pastoral mentor who will help you with spiritual formation and your character.