First of all you need to know what you mean by faith. Is it just a bunch of facts that you believe to be true - God’s sovereignty, the virgin birth, the Bible as the inspired word of God ... or does faith mean something deeper, the foundation of your life? Maybe that’s your problem right there. Just knowing or believing some facts isn’t life changing unless you let that knowledge change you. How has your faith changed your life? Point to something in your life that you know would be different if it wasn’t for your faith in God. If you are having trouble finding it, maybe you need to look deeper or take a second look at your faith.
Probably the clearest measure of faith would be what it has caused you to do. Faith is best seen in those moments when you know it wasn’t you getting it done. Someone else was in charge of you at the time, in other words, God working through you. You spoke up about God to someone, you did something you didn’t think you were capable of doing, or a situation worked out in your life and you didn’t make it happen, it just did. We speak of having the eyes of faith, that is what that means. When our eyes, tied to the physical world, can’t see a way out and yet there it is. The eyes of faith see what our physical eyes couldn’t.
How do we grow in faith? Exercise! Work your faith by living it. The Psalmist says in Psalm 34, “Taste and see that the Lord is good; blessed is the man who takes refuge in him.” Step out in faith and see if God won’t come through for you. As you find that he does you will be looking for opportunities to give God a chance to grow your faith, and in the process your faith will grow.