There are many ways to exhort someone to pray. For example, we can testify that God has commanded us to pray always, or we can describe examples from scripture and from our own experience of the blessings that come from prayers of gratitude, supplication, and inquiry. For instance, I can testify that I know that Heavenly Father answers prayers. I have received direction and comfort from words that have come into my mind, and I know by the Spirit that the words were from God.
***
We gain a testimony of any commandment of God by keeping that commandment (see John 7:17). This is true of the command that we pray always vocally and in secret. As your teacher and your friend, I promise that God will answer your prayers and that by the power of the Holy Ghost, you can know for yourself that the answers are from Him.