Pray for the Will of God

My summary:

The will of God is expressed to us in three ways.
1. Scripture
2. God's providence through a revelation to those with the gift of spiritual discernment
3. The Holy Spirit

We need to base our prayers through scripture. What we know God's will is through what he tells us in the word. We need to shape our prayers around that. Sometimes it is weird for me to tag on at the end "if it is your will". Should we know more what his will is in order to more confidently ask for what we know he wants to happen?

"Where there is no particular revelation, and Providence leaves it dark, and we know not what to pray for as we ought, we are expressly told that "the spirit helps us in our weakness," and "the Spirit himself intercedes for us and groans that words cannot express" (Romans 8:26). It is just as plain here as if it were revealed by a voice from heaven that the Spirit of God helps the people of God to pray according to the will of God when they themseles know not what they ought to pray for... ...When neither the Word nor Providence enables them to decide, let them be "filled with the Spirit," as God commands them to be. He says, "Be filled with the Spirit" (Ephesians 5:18). And He will lead their minds to those things God is willing to grant."

I don't know how this last part works. Any help?