While a number of tools and skills will help missionaries, no missionary will have them all. But some of the most fundamental tools and skills for success include:
A love for God. A great dependence on the gospel, and a despair in placing hope in one’s personal skills and gifts.
A love for people.
Right motives. Your goal is God’s glory: worship in places His worship doesn’t exist. Your worth is not driven by results, as you can’t manufacture or control them.
Evangelism and discipleship. Crossing oceans does not develop these skills in you. If you haven’t been doing it at home regularly, you won’t do it overseas. While you can’t control the results of your efforts, you can regularly practice and grow in these skills. This involves knowing the Bible well and being able to apply it to people's lives.
Sense of humor. Be able to laugh at yourself.
Flexibility. Know that you’ll do many jobs you never expected to.
Forbearance. Be an extender of much grace to those around you.