How to prepare my self for a possible calling to missions?

Pray, ask God for His leading, keep your antenna up about mission opportunities, inquire and see if you sense the Holy Spirit's leading. I myself began to feel called to long term missions many years before God actually sent me. It happened when I no longer expected it to happen. The main thing is.... keep your relationship with God fresh.

Talk to all the missionaries you meet. Find a way to correspond with a few missionaries online.
Go on a short term missionary trip.
Figure out what training you will need to get to the field.

Yes, pray, pray, pray.
I had the same calling and now ordained one of the best things I've ever done.
Youth pastor until I'm 25 - great working with people and because I'm young my services are energetic.
Listen to God and give it a shot.

I am the same. But I think that if we just allow God to just direct us, he will lead us where we need to be. I know God is calling me out on a mission I'm preparing myself to learn to be confident, and to not focus on my anxiety. After all everyone is not perfect. But I hope I have a life that is meaningful in this world. I want to please God