I wish I had known more about myself and being patient.
The following are some things nobody told me, but I'm telling you:
Boredom is real. I heard that before I left my home country. But now I have long periods of down time that I used to fill so easily at home. The first two months or so in a new place are the hardest, since you're establishing new friendships and a new pattern of life.
Knowing yourself is very important. I have been stretched a phenomenal amount, especially in the first months of my assignment. If you have any hidden personal issues, God will bring them to light. Be willing to deal with them as they come up; don't push them away. God needs to break you in order to use you.
Be teachable, and be a lifelong learner. It's easy to depend only on your ability to figure it out once you get there, since firsthand knowledge may seem more dependable than book knowledge and theories. It's not true. Know before you go.
It takes time to ease into the structure. At home, I had lots of energy to fill my day from early morning to late at night. But overseas, I tire so quickly. Realize that being stretched physically, emotionally, and spiritually as well as facing a new culture, language, and living situation wears you out. It's okay to slow down. Being a missionary is not about being superhuman and accomplishing a long list each day. Some days all you'll accomplish is a trip to the grocery store or a government office. It's about trust, obedience, and hearing the Master's voice.
I wish I had known about language learning and missionary relationships.
Most adults do not know how to handle the humiliation of learning a new language, of having people give them confused stares, just outright laughing at them, or becoming angry because you're in their country and can't speak the language. Many people in my language school suffered from loss of identity and inferiority. These were well-educated people who had been successful in their occupations back home. Now they were learning language full-time and couldn't understand why they were having such a hard time. Being smart does not guarantee that you will find learning language easy.
Never assume that you and your colleagues are going to be one big happy family. Generally you can't choose who you're going to work with, and no one is going to hit it off with everybody. So you may find that your colleagues have different interests and backgrounds that you can't relate to well. You may find that they do things that are quite irritating to you, or have major problems with anger, critical spirit, gossiping, etc. Good relationships take a lot of time and effort, but they are important.
I wish I had learned about spiritual warfare.
I wish I had known more about my relationship to God and about spiritual warfare. Victory Over the Darkness by Neil T. Anderson is one book every Christian should read. This book helps us understand and recognize spiritual warfare. Wherever we're living right now, we are in the middle of a battle. We need to understand the nature of that battle so that we can be victorious over our enemy. When we cross into another culture, where Satan has built strongholds for centuries and where cultural cues vary, the battle looks different. However, our victory over the powers of darkness is still in Christ.
Editor's Note: In addition to Neil T. Anderson's book, see also Spiritual Warfare for Every Christian by Dean Sherman.