Learn about the Unreached people groups and pray for them – see here. (The Joshua Project)
Add Scripture, especially the Psalms and New Testament passages into your prayers and pray that God will raise up laborers for the different fields and people groups – Matthew 9:36-38.
Pray for the gospel to go forth and spread rapidly and that the Word of God would be honored – 2 Thessalonians 3:1-3, and for protection for the missionary from evil men. We can ask God for protection and boldness and wisdom in dealing with certain people and areas that are extra dangerous (Islamic terrorism areas, war-torn areas – God gives us wisdom on how to be balanced. (name the country or area or people group and missionary that you are praying for. Lift the specific area, people group, and missionary to the Lord in your prayers.)
Get a list of all the missionaries your church supports and pray for them, one a day or every other day, or some kind of regular schedule. You could walk through Colossians 1:9-13 or Ephesians 3;14-21 in your prayers for them.
Pray for missionaries and their boldness and holiness and for their spiritual warfare against demonic forces – Ephesians 6:10-20.
Here is an excellent web-site called “Prayer Cast” that has a synopsis of countries, people groups, religions, and videos of scenes from that particular country or people group or religion, and usually a national believer leads you through praying for that country. You may not agree with some of the side remarks or theology that some of these Christians make, but the point is to gain a heart of praying for different areas and peoples.