What to Do for Missions? - Pray!
from a fellow missionary:

Missionaries mean it when they tell you, 'What we really need is your prayers!' We can do without money (Paul sometimes made tents), but we can't do without prayers. The 'Gospel-destitute areas' see us as criminal combatants, not friends (Colossians 4:2-4). We're up against reigning principalities, religious powers, radical politicians, and recurring persecution. We get attacked from the front, from the rear, from the sides, and, yes, even from within (2 Cor. 7:5). Missionaries aren't special. There is nothing about our foreign geography that makes us super-sanctified or sin-proof. We're tempted to deny like Peter, pout like Elijah, get cynical like Jonah, and turn back like John Mark. We deal with depression and loneliness and pain and threats and fears and danger and frustration. Our women and children get injured in the fray. Our new converts get attacked worse than we do. War is hell. So please, pray!

When you do, sure, pray for our safety (Rom. 15:30-31; 2 Thess. 3:2), but please don't exert all your time there. Jesus made it clear that mission work is exceedingly unsafe, so we're past that hump. We'd love to avoid pain, but not at the expense of boldness; Christ must be lifted up at any cost (Phil. 1:20-21). So pore over our prayer letters (and reply once in a while). And when you pray, pray the prayer that Paul requested: that the word of the Lord would spread quickly and be glorified. (2 Thess. 3:1). That's the crux of the matter. That's the reason we came.

J.O. Fraser:
"I am not asking you just to give 'help' in prayer as a sort of sideline, but I am trying to throw the main responsibility of this prayer-warfare on you. I want you to take the BURDEN of these people upon your shoulders. I want you to wrestle with God for them."