"Therefore go and make disciples of all nations, baptizing them in the name of Father and of The Son and of the Holy Spirit." -Matthew 28:19
When God calls you to go, you just go. While the anxieties of the world may begin to creep up inside of you, you just go. We serve a Father who is good and sovereign. If He wants you to go, then you will go and everything will work out in the end the way that it is supposed to. When God calls you to go, the money will come. The time will come. The location will come. The trip will come together so beautifully that you know that it had to be God himself that put it all together.
When God calls you to go, there is nothing to fear but fear itself. God already had your plan written and just, wow, is it so beautiful. God will protect you wherever you are going if you continue to place your faith in God. He is sending you to this location because this is where He needs you to help or where you need to be to be helped.
Mission trips are just so incredible because not only do you get to go and show the incredible love of your Heavenly Father, but you also get to grow as a person. At a meeting for my mission trip in March, we were told of a person in another country being approached by one of the natives. The native told them, "You know God doesn't need you here. God doesn't need you to bring Him here. God is already here. He's allowing you to be here to help, but you're not needed here." That just perfectly sums it up. When God calls you, He's not just calling you to help others. He's calling for a chance to bring you closer.
When God calls you to go, you just simply have to strap in and be prepared for the ride.