Romans 10:7

So then faith comes by hearing, and hearing by the word of God.

When we become fully persuaded by something, we believe it in our hearts.  Our faith will increase when we study the word, say it out loud until we become fully persuaded that what we are praying will come to pass.  The more we hear the word of God the more revelation we will have on the word of God, and then our FAITH will come in what we believe for.